diff --git a/dom/html/HTMLInputElement.cpp b/dom/html/HTMLInputElement.cpp
index 65aaa222f281..2b8f0f1671cd 100644
--- a/dom/html/HTMLInputElement.cpp
+++ b/dom/html/HTMLInputElement.cpp
@@ -7382,6 +7382,28 @@ HTMLInputElement::SetFilePickerFiltersFromAccept(nsIFilePicker* filePicker)
     }
   }
 
+  // Remove similar filters
+  // Iterate over a copy, as we might modify the original filters list
+  nsTArray<nsFilePickerFilter> filtersCopy;
+  filtersCopy = filters;
+  for (uint32_t i = 0; i < filtersCopy.Length(); ++i) {
+    const nsFilePickerFilter& filterToCheck = filtersCopy[i];
+    if (filterToCheck.mFilterMask) {
+      continue;
+    }
+    for (uint32_t j = 0; j < filtersCopy.Length(); ++j) {
+      if (i == j) {
+        continue;
+      }
+      if (FindInReadable(filterToCheck.mFilter, filtersCopy[j].mFilter)) {
+        // We already have a similar, less restrictive filter (i.e.
+        // filterToCheck extensionList is just a subset of another filter
+        // extension list): remove this one
+        filters.RemoveElement(filterToCheck);
+      }
+    }
+  }
+
   // Add "All Supported Types" filter
   if (filters.Length() > 1) {
     nsXPIDLString title;
diff --git a/dom/html/HTMLInputElement.h b/dom/html/HTMLInputElement.h
index 4ab26e452668..74e51ce101ee 100644
--- a/dom/html/HTMLInputElement.h
+++ b/dom/html/HTMLInputElement.h
@@ -323,6 +323,8 @@ public:
    * filter specified or not.
    * @note If more than one valid filter is found, the "All Supported Types"
    * filter is added, which is the concatenation of all valid filters.
+   * @note Duplicate filters and similar filters (i.e. filters whose file
+   * extensions already exist in another filter) are ignored.
    * @note "All Files" filter will be selected by default if unknown mime types
    * have been specified and no file extension filter has been specified.
    * Otherwise, specified filter or "All Supported Types" filter will be
diff --git a/dom/html/test/forms/test_input_file_picker.html b/dom/html/test/forms/test_input_file_picker.html
index 62ef5baa31bb..ec7f29ffdfad 100644
--- a/dom/html/test/forms/test_input_file_picker.html
+++ b/dom/html/test/forms/test_input_file_picker.html
@@ -11,6 +11,7 @@
 <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=377624">Mozilla Bug 377624</a>
 <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=565274">Mozilla Bug 565274</a>
 <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=701353">Mozilla Bug 701353</a>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=826176">Mozilla Bug 826176</a>
 <p id="display"></p>
 <div id="content">
   <input id='a' type='file' accept="image/*">
@@ -29,7 +30,10 @@
   <input id='n' type="file" accept="">
   <input id='o' type="file" accept=".test">
   <input id='p' type="file" accept="image/gif,.csv">
+  <input id='q' type="file" accept="image/gif,.gif">
   <input id='z' type='file' accept="i/am,a,pathological,;,,,,test/case">
+  <input id='mix-ref' type="file" accept="image/jpeg">
+  <input id='mix' type="file" accept="image/jpeg,.jpg">
   <input id='hidden' hidden type='file'>
   <input id='untrusted-click' type='file'>
   <input id='prevent-default' type='file'>
@@ -86,7 +90,11 @@ var testData = [["a", 1, MockFilePicker.filterImages, 1],
                 ["n", 0, undefined, 0],
                 ["o", 1, "*.test", 1],
                 ["p", 3, "*.gif; *.csv", 1],
+                ["q", 1, "*.gif", 1],
                 ["z", 0, undefined, 0],
+                // Note: mix and mix-ref tests extension lists are checked differently: see SimpleTest.executeSoon below
+                ["mix-ref", undefined, undefined, undefined],
+                ["mix", 1, undefined, 1],
                 ["hidden", 0, undefined, 0],
                 ["untrusted-click", 0, undefined, 0],
                 ["prevent-default", 0, undefined, 0, true],
@@ -109,6 +117,7 @@ var currentTest = 0;
 var filterAllAdded;
 var filters;
 var filterIndex;
+var mixRefExtensionList;
 
 // disable popups to make sure that the popup blocker does not interfere
 // with manually opened file pickers.
@@ -196,12 +205,31 @@ function runTests() {
          "File picker show method should have been called (" + testName + ")");
       ok(filterAllAdded,
          "filterAll is missing (" + testName + ")");
-      is(filters.length, testData[currentTest][1],
-         "appendFilters not called as often as expected (" + testName + ")");
-      is(filters[0], testData[currentTest][2],
-         "Correct filters should have been added (" + testName + ")");
-      is(filterIndex, testData[currentTest][3],
-         "File picker should show the correct filter index (" + testName + ")");
+      if (testName == "mix-ref") {
+        // Used only for reference for next test: nothing to be tested here
+        mixRefExtensionList = filters[0];
+        if (mixRefExtensionList == undefined) {
+          mixRefExtensionList = "";
+        }
+      } else {
+        if (testName == "mix") {
+          // Mixing mime type and file extension filters ("image/jpeg" and
+          // ".jpg" here) shouldn't restrict the list but only extend it, if file
+          // extension filter isn't a duplicate
+          ok(filters[0].contains(mixRefExtensionList),
+             "Mixing mime types and file extension filters shouldn't restrict extension list: " +
+             mixRefExtensionList + " | " + filters[0]);
+          ok(filters[0].contains("*.jpg"),
+             "Filter should contain '.jpg' extension", filters[0]);
+        } else {
+          is(filters[0], testData[currentTest][2],
+             "Correct filters should have been added (" + testName + ")");
+          is(filters.length, testData[currentTest][1],
+             "appendFilters not called as often as expected (" + testName + ")");
+        }
+        is(filterIndex, testData[currentTest][3],
+           "File picker should show the correct filter index (" + testName + ")");
+      }
 
       if (++currentTest == testData.length) {
         MockFilePicker.cleanup();