diff --git a/intl/unicharutil/util/nsUnicharUtils.cpp b/intl/unicharutil/util/nsUnicharUtils.cpp
index c0e23f1a9f64..a3baa7561056 100644
--- a/intl/unicharutil/util/nsUnicharUtils.cpp
+++ b/intl/unicharutil/util/nsUnicharUtils.cpp
@@ -162,6 +162,32 @@ void ToFoldedCase(const char16_t* aIn, char16_t* aOut, uint32_t aLen) {
   }
 }
 
+uint32_t ToNaked(uint32_t aChar) {
+  if (IS_ASCII(aChar)) {
+    return aChar;
+  }
+  return mozilla::unicode::GetNaked(aChar);
+}
+
+void ToNaked(nsAString& aString) {
+  char16_t* buf = aString.BeginWriting();
+  ToNaked(buf, buf, aString.Length());
+}
+
+void ToNaked(const char16_t* aIn, char16_t* aOut, uint32_t aLen) {
+  for (uint32_t i = 0; i < aLen; i++) {
+    uint32_t ch = aIn[i];
+    if (i < aLen - 1 && NS_IS_SURROGATE_PAIR(ch, aIn[i + 1])) {
+      ch = mozilla::unicode::GetNaked(SURROGATE_TO_UCS4(ch, aIn[i + 1]));
+      NS_ASSERTION(!IS_IN_BMP(ch), "stripping crossed BMP/SMP boundary!");
+      aOut[i++] = H_SURROGATE(ch);
+      aOut[i] = L_SURROGATE(ch);
+      continue;
+    }
+    aOut[i] = ToNaked(ch);
+  }
+}
+
 int32_t nsCaseInsensitiveStringComparator::operator()(const char16_t* lhs,
                                                       const char16_t* rhs,
                                                       uint32_t lLength,
diff --git a/intl/unicharutil/util/nsUnicharUtils.h b/intl/unicharutil/util/nsUnicharUtils.h
index 1f1d1a949ae1..ea02c5dd5aa9 100644
--- a/intl/unicharutil/util/nsUnicharUtils.h
+++ b/intl/unicharutil/util/nsUnicharUtils.h
@@ -56,6 +56,10 @@ uint32_t ToFoldedCase(uint32_t aChar);
 void ToFoldedCase(nsAString& aString);
 void ToFoldedCase(const char16_t* aIn, char16_t* aOut, uint32_t aLen);
 
+uint32_t ToNaked(uint32_t aChar);
+void ToNaked(nsAString& aString);
+void ToNaked(const char16_t* aIn, char16_t* aOut, uint32_t aLen);
+
 class nsCaseInsensitiveStringComparator : public nsStringComparator {
  public:
   nsCaseInsensitiveStringComparator() = default;
diff --git a/intl/unicharutil/util/nsUnicodeProperties.cpp b/intl/unicharutil/util/nsUnicodeProperties.cpp
index a03ffc5d5452..a8c710b71ba1 100644
--- a/intl/unicharutil/util/nsUnicodeProperties.cpp
+++ b/intl/unicharutil/util/nsUnicodeProperties.cpp
@@ -8,8 +8,12 @@
 #include "nsUnicodePropertyData.cpp"
 
 #include "mozilla/ArrayUtils.h"
+#include "mozilla/HashTable.h"
 #include "nsCharTraits.h"
 
+#include "unicode/uchar.h"
+#include "unicode/unorm2.h"
+
 #define UNICODE_BMP_LIMIT 0x10000
 #define UNICODE_LIMIT 0x110000
 
@@ -305,6 +309,80 @@ uint32_t CountGraphemeClusters(const char16_t* aText, uint32_t aLength) {
   return result;
 }
 
+uint32_t GetNaked(uint32_t aCh) {
+  using namespace mozilla;
+
+  static const UNormalizer2* normalizer;
+  static HashMap<uint32_t, uint32_t> nakedCharCache;
+
+  HashMap<uint32_t, uint32_t>::Ptr entry = nakedCharCache.lookup(aCh);
+  if (entry.found()) {
+    return entry->value();
+  }
+
+  UErrorCode error = U_ZERO_ERROR;
+  if (!normalizer) {
+    normalizer = unorm2_getNFDInstance(&error);
+    if (U_FAILURE(error)) {
+      return aCh;
+    }
+  }
+
+  static const size_t MAX_DECOMPOSITION_SIZE = 16;
+  UChar decomposition[MAX_DECOMPOSITION_SIZE];
+  UChar* combiners;
+  int32_t decompositionLen;
+  uint32_t baseChar, nextChar;
+  decompositionLen = unorm2_getDecomposition(normalizer, aCh, decomposition,
+                                             MAX_DECOMPOSITION_SIZE, &error);
+  if (decompositionLen < 1) {
+    // The character does not decompose.
+    return aCh;
+  }
+
+  if (u_getIntPropertyValue(aCh, UCHAR_GENERAL_CATEGORY) & U_GC_M_MASK) {
+    // The character is itself a combining character, and we don't want to use
+    // its decomposition into multiple combining characters.
+    baseChar = aCh;
+    goto cache;
+  }
+
+  if (NS_IS_HIGH_SURROGATE(decomposition[0])) {
+    baseChar = SURROGATE_TO_UCS4(decomposition[0], decomposition[1]);
+    combiners = decomposition + 2;
+  } else {
+    baseChar = decomposition[0];
+    combiners = decomposition + 1;
+  }
+
+  if (IS_IN_BMP(baseChar) != IS_IN_BMP(aCh)) {
+    // Mappings that would change the length of a UTF-16 string are not
+    // currently supported.
+    baseChar = aCh;
+    goto cache;
+  }
+
+  if (decompositionLen > 1) {
+    if (NS_IS_HIGH_SURROGATE(combiners[0])) {
+      nextChar = SURROGATE_TO_UCS4(combiners[0], combiners[1]);
+    } else {
+      nextChar = combiners[0];
+    }
+    if (u_getCombiningClass(nextChar) == 0) {
+      // Hangul syllables decompose but do not actually have diacritics.
+      baseChar = aCh;
+    }
+  }
+
+cache:
+  if (!nakedCharCache.putNew(aCh, baseChar)) {
+    // We're out of memory, so delete the cache to free some up.
+    nakedCharCache.clearAndCompact();
+  }
+
+  return baseChar;
+}
+
 }  // end namespace unicode
 
 }  // end namespace mozilla
diff --git a/intl/unicharutil/util/nsUnicodeProperties.h b/intl/unicharutil/util/nsUnicodeProperties.h
index 8922b1d0b436..b34a527e360a 100644
--- a/intl/unicharutil/util/nsUnicodeProperties.h
+++ b/intl/unicharutil/util/nsUnicodeProperties.h
@@ -229,6 +229,9 @@ class ClusterIterator {
 // Count the number of grapheme clusters in the given string
 uint32_t CountGraphemeClusters(const char16_t* aText, uint32_t aLength);
 
+// Remove diacritics from a character
+uint32_t GetNaked(uint32_t aCh);
+
 // A simple reverse iterator for a string of char16_t codepoints that
 // advances by Unicode grapheme clusters
 class ClusterReverseIterator {
diff --git a/mobile/android/app/mobile.js b/mobile/android/app/mobile.js
index 07bdc3c94a74..f0fb3aab3b49 100644
--- a/mobile/android/app/mobile.js
+++ b/mobile/android/app/mobile.js
@@ -236,6 +236,7 @@ pref("accessibility.typeaheadfind.flashBar", 1);
 pref("accessibility.typeaheadfind.linksonly", false);
 pref("accessibility.typeaheadfind.casesensitive", 0);
 pref("accessibility.browsewithcaret_shortcut.enabled", false);
+pref("findbar.matchdiacritics", 0);
 
 // Whether the character encoding menu is under the main Firefox button. This
 // preference is a string so that localizers can alter it.
diff --git a/mobile/android/modules/geckoview/GeckoViewContent.jsm b/mobile/android/modules/geckoview/GeckoViewContent.jsm
index b52a161861e7..684f165ea013 100644
--- a/mobile/android/modules/geckoview/GeckoViewContent.jsm
+++ b/mobile/android/modules/geckoview/GeckoViewContent.jsm
@@ -332,6 +332,7 @@ class GeckoViewContent extends GeckoViewModule {
 
     finder.caseSensitive = !!aData.matchCase;
     finder.entireWord = !!aData.wholeWord;
+    finder.matchDiacritics = !!aData.matchDiacritics;
     finder.addResultListener(this._finderListener);
 
     const drawOutline =
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 861ccd2a916d..4b0372ff5f03 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -773,6 +773,11 @@ pref("accessibility.typeaheadfind.matchesCountLimit", 1000);
 pref("findbar.highlightAll", false);
 pref("findbar.entireword", false);
 pref("findbar.iteratorTimeout", 100);
+// matchdiacritics: controls the find bar's diacritic matching
+//     0 - "never"  (ignore diacritics)
+//     1 - "always" (match diacritics)
+// other - "auto"   (match diacritics if input has diacritics, ignore otherwise)
+pref("findbar.matchdiacritics", 0);
 
 // use Mac OS X Appearance panel text smoothing setting when rendering text, disabled by default
 pref("gfx.use_text_smoothing_setting", false);
diff --git a/toolkit/actors/FinderChild.jsm b/toolkit/actors/FinderChild.jsm
index b2a084394098..7fb6f39b0f7e 100644
--- a/toolkit/actors/FinderChild.jsm
+++ b/toolkit/actors/FinderChild.jsm
@@ -28,6 +28,10 @@ class FinderChild extends JSWindowActorChild {
         this.finder.caseSensitive = data.caseSensitive;
         break;
 
+      case "Finder:MatchDiacritics":
+        this.finder.matchDiacritics = data.matchDiacritics;
+        break;
+
       case "Finder:EntireWord":
         this.finder.entireWord = data.entireWord;
         break;
diff --git a/toolkit/components/extensions/FindContent.jsm b/toolkit/components/extensions/FindContent.jsm
index 7ab732a138a4..930a3aea84c4 100644
--- a/toolkit/components/extensions/FindContent.jsm
+++ b/toolkit/components/extensions/FindContent.jsm
@@ -51,6 +51,7 @@ class FindContent {
    * @param {string} queryphrase - the text to search for.
    * @param {boolean} caseSensitive - whether to use case sensitive matches.
    * @param {boolean} includeRangeData - whether to collect and return range data.
+   * @param {boolean} matchDiacritics - whether diacritics must match.
    * @param {boolean} searchString - whether to collect and return rect data.
    *
    * @returns {object} that includes:
@@ -66,6 +67,7 @@ class FindContent {
         entireWord,
         includeRangeData,
         includeRectData,
+        matchDiacritics,
       } = params;
 
       this.iterator.reset();
@@ -77,6 +79,7 @@ class FindContent {
         entireWord: !!entireWord,
         finder: this.finder,
         listener: this.finder,
+        matchDiacritics: !!matchDiacritics,
         useSubFrames: false,
       });
 
diff --git a/toolkit/components/find/nsFind.cpp b/toolkit/components/find/nsFind.cpp
index f02296eaf613..fb04cde0f721 100644
--- a/toolkit/components/find/nsFind.cpp
+++ b/toolkit/components/find/nsFind.cpp
@@ -60,7 +60,10 @@ NS_IMPL_CYCLE_COLLECTING_RELEASE(nsFind)
 NS_IMPL_CYCLE_COLLECTION(nsFind)
 
 nsFind::nsFind()
-    : mFindBackward(false), mCaseSensitive(false), mWordBreaker(nullptr) {}
+    : mFindBackward(false),
+      mCaseSensitive(false),
+      mMatchDiacritics(false),
+      mWordBreaker(nullptr) {}
 
 nsFind::~nsFind() = default;
 
@@ -396,6 +399,22 @@ nsFind::SetEntireWord(bool aEntireWord) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsFind::GetMatchDiacritics(bool* aMatchDiacritics) {
+  if (!aMatchDiacritics) {
+    return NS_ERROR_NULL_POINTER;
+  }
+
+  *aMatchDiacritics = mMatchDiacritics;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsFind::SetMatchDiacritics(bool aMatchDiacritics) {
+  mMatchDiacritics = aMatchDiacritics;
+  return NS_OK;
+}
+
 // Here begins the find code. A ten-thousand-foot view of how it works: Find
 // needs to be able to compare across inline (but not block) nodes, e.g. find
 // for "abc" should match a<b>b</b>c. So after we've searched a node, we're not
@@ -506,6 +525,9 @@ nsFind::Find(const nsAString& aPatText, nsRange* aSearchRange,
   if (!mCaseSensitive) {
     ToFoldedCase(patAutoStr);
   }
+  if (!mMatchDiacritics) {
+    ToNaked(patAutoStr);
+  }
 
   // Ignore soft hyphens in the pattern
   static const char kShy[] = {char(CH_SHY), 0};
@@ -684,8 +706,13 @@ nsFind::Find(const nsAString& aPatText, nsRange* aSearchRange,
     }
     if (!inWhitespace && IsSpace(patc)) {
       inWhitespace = true;
-    } else if (!inWhitespace && !mCaseSensitive) {
-      c = ToFoldedCase(c);
+    } else if (!inWhitespace) {
+      if (!mCaseSensitive) {
+        c = ToFoldedCase(c);
+      }
+      if (!mMatchDiacritics) {
+        c = ToNaked(c);
+      }
     }
 
     if (c == CH_SHY) {
diff --git a/toolkit/components/find/nsFind.h b/toolkit/components/find/nsFind.h
index 76cc4537d717..37668f702709 100644
--- a/toolkit/components/find/nsFind.h
+++ b/toolkit/components/find/nsFind.h
@@ -42,6 +42,7 @@ class nsFind : public nsIFind {
   // Parameters set from the interface:
   bool mFindBackward;
   bool mCaseSensitive;
+  bool mMatchDiacritics;
 
   // Use "find entire words" mode by setting to a word breaker or null, to
   // disable "entire words" mode.
diff --git a/toolkit/components/find/nsFindService.cpp b/toolkit/components/find/nsFindService.cpp
index 1d1731787f94..7499132c2c2c 100644
--- a/toolkit/components/find/nsFindService.cpp
+++ b/toolkit/components/find/nsFindService.cpp
@@ -79,3 +79,13 @@ NS_IMETHODIMP nsFindService::SetMatchCase(bool aMatchCase) {
   mMatchCase = aMatchCase;
   return NS_OK;
 }
+
+NS_IMETHODIMP nsFindService::GetMatchDiacritics(bool* aMatchDiacritics) {
+  NS_ENSURE_ARG_POINTER(aMatchDiacritics);
+  *aMatchDiacritics = mMatchDiacritics;
+  return NS_OK;
+}
+NS_IMETHODIMP nsFindService::SetMatchDiacritics(bool aMatchDiacritics) {
+  mMatchDiacritics = aMatchDiacritics;
+  return NS_OK;
+}
diff --git a/toolkit/components/find/nsFindService.h b/toolkit/components/find/nsFindService.h
index 595b797728a7..5204076f5d91 100644
--- a/toolkit/components/find/nsFindService.h
+++ b/toolkit/components/find/nsFindService.h
@@ -40,4 +40,5 @@ class nsFindService : public nsIFindService {
   bool mWrapFind;
   bool mEntireWord;
   bool mMatchCase;
+  bool mMatchDiacritics;
 };
diff --git a/toolkit/components/find/nsIFind.idl b/toolkit/components/find/nsIFind.idl
index 6cae5dff63c7..941ed56cacc3 100644
--- a/toolkit/components/find/nsIFind.idl
+++ b/toolkit/components/find/nsIFind.idl
@@ -15,6 +15,7 @@ interface nsIFind : nsISupports
   attribute boolean findBackwards;
   attribute boolean caseSensitive;
   attribute boolean entireWord;
+  attribute boolean matchDiacritics;
 
   /**
    * Find some text in the current context. The implementation is
diff --git a/toolkit/components/find/nsIFindService.idl b/toolkit/components/find/nsIFindService.idl
index 0c1b0e215e62..f5a5e18ce653 100644
--- a/toolkit/components/find/nsIFindService.idl
+++ b/toolkit/components/find/nsIFindService.idl
@@ -22,5 +22,6 @@ interface nsIFindService : nsISupports
     attribute boolean wrapFind;
     attribute boolean entireWord;
     attribute boolean matchCase;
+    attribute boolean matchDiacritics;
 
 };
diff --git a/toolkit/components/find/nsIWebBrowserFind.idl b/toolkit/components/find/nsIWebBrowserFind.idl
index 634d39973acc..1a78ea7269a0 100644
--- a/toolkit/components/find/nsIWebBrowserFind.idl
+++ b/toolkit/components/find/nsIWebBrowserFind.idl
@@ -79,6 +79,13 @@ interface nsIWebBrowserFind : nsISupports
      */
     attribute boolean matchCase;
 
+    /**
+     * matchDiacritics
+     *
+     * Whether to match diacritics when searching. Default is false.
+     */
+    attribute boolean matchDiacritics;
+
     /**
      * searchFrames
      *
diff --git a/toolkit/components/find/nsWebBrowserFind.cpp b/toolkit/components/find/nsWebBrowserFind.cpp
index d764d0c635e8..b3dc41d1133e 100644
--- a/toolkit/components/find/nsWebBrowserFind.cpp
+++ b/toolkit/components/find/nsWebBrowserFind.cpp
@@ -50,6 +50,7 @@ nsWebBrowserFind::nsWebBrowserFind()
       mWrapFind(false),
       mEntireWord(false),
       mMatchCase(false),
+      mMatchDiacritics(false),
       mSearchSubFrames(true),
       mSearchParentFrames(true) {}
 
@@ -286,6 +287,19 @@ nsWebBrowserFind::SetMatchCase(bool aMatchCase) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsWebBrowserFind::GetMatchDiacritics(bool* aMatchDiacritics) {
+  NS_ENSURE_ARG_POINTER(aMatchDiacritics);
+  *aMatchDiacritics = mMatchDiacritics;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWebBrowserFind::SetMatchDiacritics(bool aMatchDiacritics) {
+  mMatchDiacritics = aMatchDiacritics;
+  return NS_OK;
+}
+
 void nsWebBrowserFind::SetSelectionAndScroll(nsPIDOMWindowOuter* aWindow,
                                              nsRange* aRange) {
   RefPtr<Document> doc = aWindow->GetDoc();
@@ -622,6 +636,7 @@ nsresult nsWebBrowserFind::SearchInFrame(nsPIDOMWindowOuter* aWindow,
   NS_ENSURE_SUCCESS(rv, rv);
 
   (void)find->SetCaseSensitive(mMatchCase);
+  (void)find->SetMatchDiacritics(mMatchDiacritics);
   (void)find->SetFindBackwards(mFindBackwards);
 
   (void)find->SetEntireWord(mEntireWord);
diff --git a/toolkit/components/find/nsWebBrowserFind.h b/toolkit/components/find/nsWebBrowserFind.h
index f886b66fd847..d6d5596e2ce5 100644
--- a/toolkit/components/find/nsWebBrowserFind.h
+++ b/toolkit/components/find/nsWebBrowserFind.h
@@ -79,6 +79,7 @@ class nsWebBrowserFind : public nsIWebBrowserFind,
   bool mWrapFind;
   bool mEntireWord;
   bool mMatchCase;
+  bool mMatchDiacritics;
 
   bool mSearchSubFrames;
   bool mSearchParentFrames;
diff --git a/toolkit/components/typeaheadfind/nsITypeAheadFind.idl b/toolkit/components/typeaheadfind/nsITypeAheadFind.idl
index 9bfb39874921..2f94136e72bf 100644
--- a/toolkit/components/typeaheadfind/nsITypeAheadFind.idl
+++ b/toolkit/components/typeaheadfind/nsITypeAheadFind.idl
@@ -70,6 +70,7 @@ interface nsITypeAheadFind : nsISupports
   readonly attribute AString searchString;
                                         // Most recent search string
   attribute boolean caseSensitive;      // Searches are case sensitive
+  attribute boolean matchDiacritics;    // Searches preserve diacritics
   attribute boolean entireWord;         // Search for whole words only
   readonly attribute Element foundLink;
                                         // Most recent elem found, if a link
diff --git a/toolkit/components/typeaheadfind/nsTypeAheadFind.cpp b/toolkit/components/typeaheadfind/nsTypeAheadFind.cpp
index 7d204a7f8cde..ee0fc644626a 100644
--- a/toolkit/components/typeaheadfind/nsTypeAheadFind.cpp
+++ b/toolkit/components/typeaheadfind/nsTypeAheadFind.cpp
@@ -79,7 +79,8 @@ nsTypeAheadFind::nsTypeAheadFind()
       mLastFindLength(0),
       mIsSoundInitialized(false),
       mCaseSensitive(false),
-      mEntireWord(false) {}
+      mEntireWord(false),
+      mMatchDiacritics(false) {}
 
 nsTypeAheadFind::~nsTypeAheadFind() {
   nsCOMPtr<nsIPrefBranch> prefInternal(
@@ -204,6 +205,24 @@ nsTypeAheadFind::GetEntireWord(bool* isEntireWord) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsTypeAheadFind::SetMatchDiacritics(bool matchDiacritics) {
+  mMatchDiacritics = matchDiacritics;
+
+  if (mFind) {
+    mFind->SetMatchDiacritics(mMatchDiacritics);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsTypeAheadFind::GetMatchDiacritics(bool* matchDiacritics) {
+  *matchDiacritics = mMatchDiacritics;
+
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsTypeAheadFind::SetDocShell(nsIDocShell* aDocShell) {
   mDocShell = do_GetWeakReference(aDocShell);
diff --git a/toolkit/components/typeaheadfind/nsTypeAheadFind.h b/toolkit/components/typeaheadfind/nsTypeAheadFind.h
index 6dbbeac9fcc3..ffe450874390 100644
--- a/toolkit/components/typeaheadfind/nsTypeAheadFind.h
+++ b/toolkit/components/typeaheadfind/nsTypeAheadFind.h
@@ -118,6 +118,7 @@ class nsTypeAheadFind : public nsITypeAheadFind,
 
   bool mCaseSensitive;
   bool mEntireWord;
+  bool mMatchDiacritics;
 
   bool EnsureFind() {
     if (mFind) {
@@ -131,6 +132,7 @@ class nsTypeAheadFind : public nsITypeAheadFind,
 
     mFind->SetCaseSensitive(mCaseSensitive);
     mFind->SetEntireWord(mEntireWord);
+    mFind->SetMatchDiacritics(mMatchDiacritics);
 
     return true;
   }
diff --git a/toolkit/components/windowcreator/test/test_nsFind.html b/toolkit/components/windowcreator/test/test_nsFind.html
index 9689d21a219c..0e6ebcacab1f 100644
--- a/toolkit/components/windowcreator/test/test_nsFind.html
+++ b/toolkit/components/windowcreator/test/test_nsFind.html
@@ -1,6 +1,7 @@
 <!DOCTYPE HTML>
 <html>
 <!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=202251
 https://bugzilla.mozilla.org/show_bug.cgi?id=450048
 https://bugzilla.mozilla.org/show_bug.cgi?id=969980
 https://bugzilla.mozilla.org/show_bug.cgi?id=1589786
@@ -13,7 +14,6 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1589786
 
 <script type="application/javascript">
 
-/** Test for Bug 450048 **/
 SimpleTest.waitForExplicitFinish();
 
 async function runTests() {
@@ -47,15 +47,20 @@ async function runTests() {
   rf.findBackwards = false;
 
   rf.caseSensitive = false;
+  rf.matchDiacritics = false;
 
   searchValue = "TexT";
   retRange = rf.Find(searchValue, searchRange, startPt, endPt);
   ok(retRange, "\"" + searchValue + "\" not found (not caseSensitive)");
 
-  searchValue = "λόγος";
+  searchValue = "λογος";
   retRange = rf.Find(searchValue, searchRange, startPt, endPt);
   ok(retRange, "\"" + searchValue + "\" not found (not caseSensitive)");
 
+  searchValue = "유";
+  retRange = rf.Find(searchValue, searchRange, startPt, endPt);
+  ok(!retRange, "\"" + searchValue + "\" found (not caseSensitive)");
+
   searchValue = "degrees k";
   retRange = rf.Find(searchValue, searchRange, startPt, endPt);
   ok(retRange, "\"" + searchValue + "\" not found (not caseSensitive)");
@@ -64,9 +69,15 @@ async function runTests() {
   retRange = rf.Find(searchValue, searchRange, startPt, endPt);
   ok(retRange, "\"" + searchValue + "\" not found (not caseSensitive)");
 
+  rf.matchDiacritics = true;
+
+  searchValue = "λογος";
+  retRange = rf.Find(searchValue, searchRange, startPt, endPt);
+  ok(!retRange, "\"" + searchValue + "\" found (not caseSensitive)");
+
   rf.caseSensitive = true;
 
-  // searchValue = "TexT";
+  searchValue = "TexT";
   retRange = rf.Find(searchValue, searchRange, startPt, endPt);
   ok(!retRange, "\"" + searchValue + "\" found (caseSensitive)");
 
@@ -267,6 +278,7 @@ async function runTests() {
 <p id="nullcharsnative">native null&#0;</p>
 <p id="nullcharsinjected"></p>
 <p id="greek">ΛΌΓΟΣ</p>
+<p id="korean">위</p>
 <p id="kelvin">degrees &#x212A;</p>
 <p id="deseret">𐐐𐐯𐑊𐐬 𐐶𐐯𐑉𐑊𐐼!</p>
 <div id="content" style="display: none">
diff --git a/toolkit/content/tests/chrome/findbar_events_window.xhtml b/toolkit/content/tests/chrome/findbar_events_window.xhtml
index c81e0763e569..3cfbe2673139 100644
--- a/toolkit/content/tests/chrome/findbar_events_window.xhtml
+++ b/toolkit/content/tests/chrome/findbar_events_window.xhtml
@@ -60,6 +60,7 @@
       await testFind();
       await testFindAgain();
       await testCaseSensitivity();
+      await testDiacriticMatching();
       await testHighlight();
     }
 
@@ -143,6 +144,24 @@
       await ContentTask.spawn(gBrowser, null, () => content.getSelection().removeAllRanges());
     }
 
+    async function testDiacriticMatching() {
+      info("Testing normal diacritic matching.");
+      let promise = once(gFindBar, "finddiacriticmatchingchange", false);
+
+      let matchDiacriticsCheckbox = gFindBar.getElement("find-match-diacritics");
+      matchDiacriticsCheckbox.click();
+
+      let e = await promise;
+      ok(e.detail.matchDiacritics, "find should match diacritics");
+
+      // Toggle it back to the original setting.
+      matchDiacriticsCheckbox.click();
+
+      // Changing diacritic matching does the search so clear the selected text
+      // before the next test.
+      await ContentTask.spawn(gBrowser, null, () => content.getSelection().removeAllRanges());
+    }
+
     async function testHighlight() {
       info("Testing find with highlight all.");
       // Update the find state so the highlight button is clickable.
diff --git a/toolkit/content/tests/chrome/findbar_window.xhtml b/toolkit/content/tests/chrome/findbar_window.xhtml
index 1f93e1a82e07..f2908ab2166b 100644
--- a/toolkit/content/tests/chrome/findbar_window.xhtml
+++ b/toolkit/content/tests/chrome/findbar_window.xhtml
@@ -28,7 +28,7 @@
 
     const SAMPLE_URL = "http://www.mozilla.org/";
     const SAMPLE_TEXT = "Some text in a text field.";
-    const SEARCH_TEXT = "Text Test";
+    const SEARCH_TEXT = "Text Test (δοκιμή)";
     const NOT_FOUND_TEXT = "This text is not on the page."
     const ITERATOR_TIMEOUT = gPrefsvc.getIntPref("findbar.iteratorTimeout");
 
@@ -88,7 +88,7 @@
       await new Promise(resolve => setTimeout(resolve, 1000));
 
       let promise = BrowserTestUtils.browserLoaded(gBrowser);
-      BrowserTestUtils.loadURI(gBrowser, "data:text/html,<h2 id='h2'>" + SEARCH_TEXT +
+      BrowserTestUtils.loadURI(gBrowser, "data:text/html;charset=utf-8,<h2 id='h2'>" + SEARCH_TEXT +
         "</h2><h2><a href='" + SAMPLE_URL + "'>Link Test</a></h2><input id='text' type='text' value='" +
         SAMPLE_TEXT + "'></input><input id='button' type='button'></input><img id='img' width='50' height='50'/>",
         { triggeringPrincipal: window.document.nodePrincipal });
@@ -735,6 +735,24 @@
       ok(gFindBar.hidden, "Successful Find Again leaves the find bar closed.");
     }
 
+    async function testToggleDiacriticMatching() {
+      await openFindbar();
+      let promise = promiseFindResult();
+      await enterStringIntoFindField("δοκιμη", false);
+      let result = await promise;
+      is(result.result, Ci.nsITypeAheadFind.FIND_FOUND, "Text should be found");
+
+      await new Promise(resolve => setTimeout(resolve, ITERATOR_TIMEOUT + 20));
+      promise = promiseFindResult();
+      let check = gFindBar.getElement("find-match-diacritics");
+      check.click();
+      result = await promise;
+      is(result.result, Ci.nsITypeAheadFind.FIND_NOTFOUND, "Text should NOT be found");
+
+      check.click();
+      gFindBar.close(true);
+    }
+
     async function testToggleEntireWord() {
       await openFindbar();
       let promise = promiseFindResult();
diff --git a/toolkit/content/widgets/findbar.js b/toolkit/content/widgets/findbar.js
index 35d5d27f8426..8f16b347e0d8 100644
--- a/toolkit/content/widgets/findbar.js
+++ b/toolkit/content/widgets/findbar.js
@@ -30,6 +30,7 @@
   ]);
   const PREFS_TO_OBSERVE_INT = new Map([
     ["typeAheadCaseSensitive", "accessibility.typeaheadfind.casesensitive"],
+    ["matchDiacritics", "findbar.matchdiacritics"],
   ]);
   const PREFS_TO_OBSERVE_ALL = new Map([
     ...PREFS_TO_OBSERVE_BOOL,
@@ -72,9 +73,12 @@
           data-l10n-id="findbar-highlight-all2" oncommand="toggleHighlight(this.checked);" type="checkbox" />
         <toolbarbutton anonid="find-case-sensitive" class="findbar-case-sensitive findbar-button tabbable"
           data-l10n-id="findbar-case-sensitive" oncommand="_setCaseSensitivity(this.checked ? 1 : 0);" type="checkbox" />
+        <toolbarbutton anonid="find-match-diacritics" class="findbar-match-diacritics findbar-button tabbable"
+          data-l10n-id="findbar-match-diacritics" oncommand="_setDiacriticMatching(this.checked ? 1 : 0);" type="checkbox" />
         <toolbarbutton anonid="find-entire-word" class="findbar-entire-word findbar-button tabbable"
           data-l10n-id="findbar-entire-word" oncommand="toggleEntireWord(this.checked);" type="checkbox" />
         <label anonid="match-case-status" class="findbar-find-fast" />
+        <label anonid="match-diacritics-status" class="findbar-find-fast" />
         <label anonid="entire-word-status" class="findbar-find-fast" />
         <label anonid="found-matches" class="findbar-find-fast found-matches" hidden="true" />
         <image anonid="find-status-icon" class="findbar-find-fast find-status-icon" />
@@ -390,6 +394,9 @@
         case "findbar.highlightAll":
           this.toggleHighlight(prefsvc.getBoolPref(prefName), true);
           break;
+        case "findbar.matchdiacritics":
+          this._setDiacriticMatching(prefsvc.getIntPref(prefName));
+          break;
         case "findbar.modalHighlight":
           this._useModalHighlight = prefsvc.getBoolPref(prefName);
           if (this.browser.finder) {
@@ -598,6 +605,55 @@
       this._dispatchFindEvent("casesensitivitychange");
     }
 
+    /**
+     * Updates the diacritic-matching mode of the findbar and its UI.
+     *
+     * @param {String} [str] The string for which diacritic matching might be
+     *                       turned on. This is only used when diacritic
+     *                       matching is in auto mode, see
+     *                       `_shouldMatchDiacritics`. The default value for
+     *                       this parameter is the find-field value.
+     * @see _shouldMatchDiacritics.
+     */
+    _updateDiacriticMatching(str) {
+      let val = str || this._findField.value;
+
+      let matchDiacritics = this._shouldMatchDiacritics(val);
+      let checkbox = this.getElement("find-match-diacritics");
+      let statusLabel = this.getElement("match-diacritics-status");
+      checkbox.checked = matchDiacritics;
+
+      statusLabel.value = matchDiacritics ? this._matchDiacriticsStr : "";
+
+      // Show the checkbox on the full Find bar in non-auto mode.
+      // Show the label in all other cases.
+      let hideCheckbox =
+        this.findMode != this.FIND_NORMAL ||
+        (this._matchDiacritics != 0 && this._matchDiacritics != 1);
+      checkbox.hidden = hideCheckbox;
+      statusLabel.hidden = !hideCheckbox;
+
+      this.browser.finder.matchDiacritics = matchDiacritics;
+    }
+
+    /**
+     * Sets the findbar diacritic-matching mode
+     * @param {Number} diacriticMatching 0 - ignore diacritics,
+     *                                   1 - match diacritics,
+     *                                   2 - auto = match diacritics if the
+     *                                       matching string contains
+     *                                       diacritics.
+     * @see _shouldMatchDiacritics
+     */
+    _setDiacriticMatching(diacriticMatching) {
+      this._matchDiacritics = diacriticMatching;
+      this._updateDiacriticMatching();
+      this._findFailedString = null;
+      this._find();
+
+      this._dispatchFindEvent("diacriticmatchingchange");
+    }
+
     /**
      * Updates the entire-word mode of the findbar and its UI.
      */
@@ -659,6 +715,7 @@
         this._fastFindStr = bundle.GetStringFromName("FastFind");
         this._fastFindLinksStr = bundle.GetStringFromName("FastFindLinks");
         this._caseSensitiveStr = bundle.GetStringFromName("CaseSensitive");
+        this._matchDiacriticsStr = bundle.GetStringFromName("MatchDiacritics");
         this._entireWordStr = bundle.GetStringFromName("EntireWord");
       }
 
@@ -783,6 +840,17 @@
       return str != str.toLowerCase();
     }
 
+    _shouldMatchDiacritics(str) {
+      if (this._matchDiacritics == 0) {
+        return false;
+      }
+      if (this._matchDiacritics == 1) {
+        return true;
+      }
+
+      return str != str.normalize("NFD");
+    }
+
     onMouseUp() {
       if (!this.hidden && this.findMode != this.FIND_NORMAL) {
         this.close();
@@ -884,6 +952,7 @@
       ).hidden = showMinimalUI;
       foundMatches.hidden = showMinimalUI || !foundMatches.value;
       this._updateCaseSensitivity();
+      this._updateDiacriticMatching();
       this._setEntireWord();
       this._setHighlightAll();
 
@@ -933,6 +1002,7 @@
 
         this._enableFindButtons(val);
         this._updateCaseSensitivity(val);
+        this._updateDiacriticMatching(val);
         this._setEntireWord();
 
         this.browser.finder.fastFind(
@@ -1026,6 +1096,7 @@
       event.initCustomEvent("find" + type, true, true, {
         query: this._findField.value,
         caseSensitive: !!this._typeAheadCaseSensitive,
+        matchDiacritics: !!this._matchDiacritics,
         entireWord: this._entireWord,
         highlightAll: this._highlightAll,
         findPrevious,
diff --git a/toolkit/locales/en-US/chrome/global/findbar.properties b/toolkit/locales/en-US/chrome/global/findbar.properties
index abe037ba7328..735941afd862 100644
--- a/toolkit/locales/en-US/chrome/global/findbar.properties
+++ b/toolkit/locales/en-US/chrome/global/findbar.properties
@@ -10,6 +10,7 @@ NormalFind=Find in page
 FastFind=Quick find
 FastFindLinks=Quick find (links only)
 CaseSensitive=(Case sensitive)
+MatchDiacritics=(Matching diacritics)
 EntireWord=(Whole words only)
 # LOCALIZATION NOTE (FoundMatches): Semicolon-separated list of plural forms.
 # See: http://developer.mozilla.org/en/docs/Localization_and_Plurals
diff --git a/toolkit/locales/en-US/toolkit/main-window/findbar.ftl b/toolkit/locales/en-US/toolkit/main-window/findbar.ftl
index 88d19168abd4..f7c59092faa0 100644
--- a/toolkit/locales/en-US/toolkit/main-window/findbar.ftl
+++ b/toolkit/locales/en-US/toolkit/main-window/findbar.ftl
@@ -25,6 +25,11 @@ findbar-case-sensitive =
     .accesskey = C
     .tooltiptext = Search with case sensitivity
 
+findbar-match-diacritics =
+    .label = Match Diacritics
+    .accesskey = D
+    .tooltiptext = Distinguish between accented letters and their base letters (for example, when searching for “resume”, “résumé” will not be matched)
+
 findbar-entire-word =
     .label = Whole Words
     .accesskey = W
diff --git a/toolkit/modules/Finder.jsm b/toolkit/modules/Finder.jsm
index ec2240c2e433..4c805383e0d2 100644
--- a/toolkit/modules/Finder.jsm
+++ b/toolkit/modules/Finder.jsm
@@ -170,6 +170,14 @@ Finder.prototype = {
     this.iterator.reset();
   },
 
+  set matchDiacritics(aMatchDiacritics) {
+    if (this._fastFind.matchDiacritics === aMatchDiacritics) {
+      return;
+    }
+    this._fastFind.matchDiacritics = aMatchDiacritics;
+    this.iterator.reset();
+  },
+
   set entireWord(aEntireWord) {
     if (this._fastFind.entireWord === aEntireWord) {
       return;
@@ -341,6 +349,7 @@ Finder.prototype = {
         caseSensitive: this._fastFind.caseSensitive,
         entireWord: this._fastFind.entireWord,
         linksOnly: aArgs.linksOnly,
+        matchDiacritics: this._fastFind.matchDiacritics,
         word: aArgs.searchString,
         useSubFrames: aArgs.useSubFrames,
       })
@@ -589,6 +598,7 @@ Finder.prototype = {
       caseSensitive: this._fastFind.caseSensitive,
       entireWord: this._fastFind.entireWord,
       linksOnly: aLinksOnly,
+      matchDiacritics: this._fastFind.matchDiacritics,
       word: aWord,
       useSubFrames: aUseSubFrames,
     };
diff --git a/toolkit/modules/FinderHighlighter.jsm b/toolkit/modules/FinderHighlighter.jsm
index 61bdbc133d5e..3dec6de936c5 100644
--- a/toolkit/modules/FinderHighlighter.jsm
+++ b/toolkit/modules/FinderHighlighter.jsm
@@ -284,6 +284,7 @@ FinderHighlighter.prototype = {
         word,
         finder: this.finder,
         listener: this,
+        matchDiacritics: this.finder._fastFind.matchDiacritics,
         useCache: true,
         useSubFrames,
         window,
diff --git a/toolkit/modules/FinderIterator.jsm b/toolkit/modules/FinderIterator.jsm
index 7eb1bcb38c5d..f77ac95703d2 100644
--- a/toolkit/modules/FinderIterator.jsm
+++ b/toolkit/modules/FinderIterator.jsm
@@ -88,6 +88,8 @@ FinderIterator.prototype = {
    *                                           - onIteratorReset();
    *                                           - onIteratorRestart({Object} iterParams);
    *                                           - onIteratorStart({Object} iterParams);
+   * @param {Boolean} options.matchDiacritics Whether to search in
+   *                                          diacritic-matching mode
    * @param {Boolean} [options.useCache]        Whether to allow results already
    *                                            present in the cache or demand fresh.
    *                                            Optional, defaults to `false`.
@@ -104,6 +106,7 @@ FinderIterator.prototype = {
     limit,
     linksOnly,
     listener,
+    matchDiacritics,
     useCache,
     word,
     useSubFrames,
@@ -132,6 +135,9 @@ FinderIterator.prototype = {
     if (typeof entireWord != "boolean") {
       throw new Error("Missing required option 'entireWord'");
     }
+    if (typeof matchDiacritics != "boolean") {
+      throw new Error("Missing required option 'matchDiacritics'");
+    }
     if (!finder) {
       throw new Error("Missing required option 'finder'");
     }
@@ -158,6 +164,7 @@ FinderIterator.prototype = {
       caseSensitive,
       entireWord,
       linksOnly,
+      matchDiacritics,
       useCache,
       window,
       word,
@@ -304,6 +311,8 @@ FinderIterator.prototype = {
    * @param {Boolean}  options.entireWord    Whether to search in entire-word mode
    * @param  {Boolean} options.linksOnly     Whether to search for the word to be
    *                                         present in links only
+   * @param {Boolean}  options.matchDiacritics Whether to search in
+   *                                           diacritic-matching mode
    * @param  {String}  options.word          The word being searched for
    * @param  (Boolean) options.useSubFrames  Whether to search subframes
    * @return {Boolean}
@@ -312,6 +321,7 @@ FinderIterator.prototype = {
     caseSensitive,
     entireWord,
     linksOnly,
+    matchDiacritics,
     word,
     useSubFrames,
   }) {
@@ -320,6 +330,7 @@ FinderIterator.prototype = {
       this._currentParams.caseSensitive === caseSensitive &&
       this._currentParams.entireWord === entireWord &&
       this._currentParams.linksOnly === linksOnly &&
+      this._currentParams.matchDiacritics === matchDiacritics &&
       this._currentParams.word == word &&
       this._currentParams.useSubFrames == useSubFrames
     );
@@ -374,6 +385,8 @@ FinderIterator.prototype = {
    * @param  {Boolean} options.entireWord    Whether to search in entire-word mode
    * @param  {Boolean} options.linksOnly     Whether to search for the word to be
    *                                         present in links only
+   * @param  {Boolean} options.matchDiacritics Whether to search in
+   *                                           diacritic-matching mode
    * @param  {Boolean} options.useCache      Whether the consumer wants to use the
    *                                         cached previous result at all
    * @param  {String}  options.word          The word being searched for
@@ -383,6 +396,7 @@ FinderIterator.prototype = {
     caseSensitive,
     entireWord,
     linksOnly,
+    matchDiacritics,
     useCache,
     word,
   }) {
@@ -392,6 +406,7 @@ FinderIterator.prototype = {
         caseSensitive,
         entireWord,
         linksOnly,
+        matchDiacritics,
         word,
       }) &&
       this._previousRanges.length
@@ -415,6 +430,7 @@ FinderIterator.prototype = {
       paramSet1.caseSensitive === paramSet2.caseSensitive &&
       paramSet1.entireWord === paramSet2.entireWord &&
       paramSet1.linksOnly === paramSet2.linksOnly &&
+      paramSet1.matchDiacritics === paramSet2.matchDiacritics &&
       paramSet1.window === paramSet2.window &&
       paramSet1.useSubFrames === paramSet2.useSubFrames &&
       NLP.levenshtein(paramSet1.word, paramSet2.word) <= allowDistance
@@ -624,11 +640,16 @@ FinderIterator.prototype = {
    *                                             sensitive mode
    * @param {Boolean}      options.entireWord    Whether to search in entire-word
    *                                             mode
+   * @param {Boolean}      options.matchDiacritics Whether to search in
+   *                                               diacritic-matching mode
    * @param {String}       options.word          The word to search for
    * @param {nsIDOMWindow} window                The window to search in
    * @yield {Range}
    */
-  *_iterateDocument({ caseSensitive, entireWord, word }, window) {
+  *_iterateDocument(
+    { caseSensitive, entireWord, matchDiacritics, word },
+    window
+  ) {
     let doc = window.document;
     let body = doc.body || doc.documentElement;
 
@@ -652,6 +673,7 @@ FinderIterator.prototype = {
       .QueryInterface(Ci.nsIFind);
     nsIFind.caseSensitive = caseSensitive;
     nsIFind.entireWord = entireWord;
+    nsIFind.matchDiacritics = matchDiacritics;
 
     while ((retRange = nsIFind.Find(word, searchRange, startPt, endPt))) {
       yield retRange;
diff --git a/toolkit/modules/FinderParent.jsm b/toolkit/modules/FinderParent.jsm
index d9c897ff536b..4626bc51aa4e 100644
--- a/toolkit/modules/FinderParent.jsm
+++ b/toolkit/modules/FinderParent.jsm
@@ -217,6 +217,12 @@ FinderParent.prototype = {
     });
   },
 
+  set matchDiacritics(aMatchDiacritics) {
+    this.sendMessageToAllContexts("Finder:MatchDiacritics", {
+      matchDiacritics: aMatchDiacritics,
+    });
+  },
+
   async setSearchStringToSelection() {
     return this.setToSelection("Finder:SetSearchStringToSelection", false);
   },
diff --git a/toolkit/modules/tests/xpcshell/test_FinderIterator.js b/toolkit/modules/tests/xpcshell/test_FinderIterator.js
index e51592c08e7f..7cc06f04c154 100644
--- a/toolkit/modules/tests/xpcshell/test_FinderIterator.js
+++ b/toolkit/modules/tests/xpcshell/test_FinderIterator.js
@@ -58,6 +58,7 @@ add_task(async function test_start() {
         Assert.equal(range.toString(), findText, "Text content should match");
       },
     },
+    matchDiacritics: false,
     word: findText,
   });
 
@@ -88,6 +89,7 @@ add_task(async function test_subframes() {
         Assert.equal(range.toString(), findText, "Text content should match");
       },
     },
+    matchDiacritics: false,
     word: findText,
     useSubFrames: true,
   });
@@ -119,6 +121,7 @@ add_task(async function test_valid_arguments() {
         ++count;
       },
     },
+    matchDiacritics: false,
     word: findText,
   });
 
@@ -137,6 +140,7 @@ add_task(async function test_valid_arguments() {
             ++count;
           },
         },
+        matchDiacritics: false,
         word: findText,
       }),
     /Missing required option 'caseSensitive'/,
@@ -144,6 +148,23 @@ add_task(async function test_valid_arguments() {
   );
   finderIterator.reset();
 
+  Assert.throws(
+    () =>
+      finderIterator.start({
+        caseSensitive: false,
+        entireWord: false,
+        listener: {
+          onIteratorRangeFound(range) {
+            ++count;
+          },
+        },
+        word: findText,
+      }),
+    /Missing required option 'matchDiacritics'/,
+    "Should throw when missing an argument"
+  );
+  finderIterator.reset();
+
   Assert.throws(
     () =>
       finderIterator.start({
@@ -153,6 +174,7 @@ add_task(async function test_valid_arguments() {
             ++count;
           },
         },
+        matchDiacritics: false,
         word: findText,
       }),
     /Missing required option 'entireWord'/,
@@ -170,6 +192,7 @@ add_task(async function test_valid_arguments() {
             ++count;
           },
         },
+        matchDiacritics: false,
         word: findText,
       }),
     /Missing required option 'finder'/,
@@ -183,6 +206,7 @@ add_task(async function test_valid_arguments() {
         caseSensitive: true,
         entireWord: false,
         finder: gMockFinder,
+        matchDiacritics: false,
         word: findText,
       }),
     /Missing valid, required option 'listener'/,
@@ -201,6 +225,7 @@ add_task(async function test_valid_arguments() {
             ++count;
           },
         },
+        matchDiacritics: false,
       }),
     /Missing required option 'word'/,
     "Should throw when missing an argument"
@@ -225,6 +250,7 @@ add_task(async function test_stop() {
         ++count;
       },
     },
+    matchDiacritics: false,
     word: findText,
   });
 
@@ -252,6 +278,7 @@ add_task(async function test_reset() {
         ++count;
       },
     },
+    matchDiacritics: false,
     word: findText,
   });
 
@@ -294,10 +321,11 @@ add_task(async function test_parallel_starts() {
         ++count;
       },
     },
+    matchDiacritics: false,
     word: findText,
   });
 
-  await new Promise(resolve => gMockWindow.setTimeout(resolve, 120));
+  await new Promise(resolve => gMockWindow.setTimeout(resolve, 100));
   Assert.ok(finderIterator.running, "We ought to be running here");
 
   let count2 = 0;
@@ -310,6 +338,7 @@ add_task(async function test_parallel_starts() {
         ++count2;
       },
     },
+    matchDiacritics: false,
     word: findText,
   });
 
@@ -360,6 +389,7 @@ add_task(async function test_allowDistance() {
         ++count;
       },
     },
+    matchDiacritics: false,
     word: findText,
   });
 
@@ -373,6 +403,7 @@ add_task(async function test_allowDistance() {
         ++count2;
       },
     },
+    matchDiacritics: false,
     word: "gu",
   });
 
@@ -387,6 +418,7 @@ add_task(async function test_allowDistance() {
         ++count3;
       },
     },
+    matchDiacritics: false,
     word: "gu",
   });