diff --git a/gfx/thebes/gfxFcPlatformFontList.cpp b/gfx/thebes/gfxFcPlatformFontList.cpp
index 266530b02c04..93575c874010 100644
--- a/gfx/thebes/gfxFcPlatformFontList.cpp
+++ b/gfx/thebes/gfxFcPlatformFontList.cpp
@@ -920,8 +920,35 @@ gfxFontConfigFont::GetGlyphRenderingOptions(const TextRunDrawParams* aRunParams)
 }
 #endif
 
+gfxFcPlatformFontList::gfxFcPlatformFontList()
+    : mLocalNames(64), mGenericMappings(32), mLastConfig(nullptr)
+{
+    // if the rescan interval is set, start the timer
+    int rescanInterval = FcConfigGetRescanInterval(nullptr);
+    if (rescanInterval) {
+        mLastConfig = FcConfigGetCurrent();
+        mCheckFontUpdatesTimer = do_CreateInstance("@mozilla.org/timer;1");
+        if (mCheckFontUpdatesTimer) {
+            mCheckFontUpdatesTimer->
+                InitWithFuncCallback(CheckFontUpdates, this,
+                                     (rescanInterval + 1) * 1000,
+                                     nsITimer::TYPE_REPEATING_SLACK);
+        } else {
+            NS_WARNING("Failure to create font updates timer");
+        }
+    }
+
+#ifdef MOZ_BUNDLED_FONTS
+    mBundledFontsInitialized = false;
+#endif
+}
+
 gfxFcPlatformFontList::~gfxFcPlatformFontList()
 {
+    if (mCheckFontUpdatesTimer) {
+        mCheckFontUpdatesTimer->Cancel();
+        mCheckFontUpdatesTimer = nullptr;
+    }
 }
 
 void
@@ -1008,6 +1035,8 @@ gfxFcPlatformFontList::AddFontSetFamilies(FcFontSet* aFontSet)
 nsresult
 gfxFcPlatformFontList::InitFontList()
 {
+    mLastConfig = FcConfigGetCurrent();
+
     // reset font lists
     gfxPlatformFontList::InitFontList();
 
@@ -1394,6 +1423,21 @@ gfxFcPlatformFontList::FindGenericFamily(const nsAString& aGeneric,
     return genericFamily;
 }
 
+/* static */ void
+gfxFcPlatformFontList::CheckFontUpdates(nsITimer *aTimer, void *aThis)
+{
+    // check for font updates
+    FcInitBringUptoDate();
+
+    // update fontlist if current config changed
+    gfxFcPlatformFontList *pfl = static_cast<gfxFcPlatformFontList*>(aThis);
+    FcConfig* current = FcConfigGetCurrent();
+    if (current != pfl->GetLastConfig()) {
+        pfl->UpdateFontList();
+        pfl->ForceGlobalReflow();
+    }
+}
+
 #ifdef MOZ_BUNDLED_FONTS
 void
 gfxFcPlatformFontList::ActivateBundledFonts()
diff --git a/gfx/thebes/gfxFcPlatformFontList.h b/gfx/thebes/gfxFcPlatformFontList.h
index b17b61801f86..b10f76b4e6f9 100644
--- a/gfx/thebes/gfxFcPlatformFontList.h
+++ b/gfx/thebes/gfxFcPlatformFontList.h
@@ -28,6 +28,13 @@ public:
     static void Release(FcObjectSet *ptr) { FcObjectSetDestroy(ptr); }
 };
 
+template <>
+class nsAutoRefTraits<FcConfig> : public nsPointerRefTraits<FcConfig>
+{
+public:
+    static void Release(FcConfig *ptr) { FcConfigDestroy(ptr); }
+    static void AddRef(FcConfig *ptr) { FcConfigReference(ptr); }
+};
 
 // Helper classes used for clearning out user font data when cairo font
 // face is destroyed. Since multiple faces may use the same data, be
@@ -187,13 +194,7 @@ protected:
 
 class gfxFcPlatformFontList : public gfxPlatformFontList {
 public:
-    gfxFcPlatformFontList()
-        : mLocalNames(64), mGenericMappings(32)
-    {
-#ifdef MOZ_BUNDLED_FONTS
-        mBundledFontsInitialized = false;
-#endif
-    }
+    gfxFcPlatformFontList();
 
     // initialize font lists
     nsresult InitFontList() override;
@@ -223,6 +224,8 @@ public:
     bool GetStandardFamilyName(const nsAString& aFontName,
                                nsAString& aFamilyName) override;
 
+    FcConfig* GetLastConfig() const { return mLastConfig; }
+
     static FT_Library GetFTLibrary();
 
 protected:
@@ -236,6 +239,8 @@ protected:
     gfxFontFamily* FindGenericFamily(const nsAString& aGeneric,
                                      nsIAtom* aLanguage);
 
+    static void CheckFontUpdates(nsITimer *aTimer, void *aThis);
+
 #ifdef MOZ_BUNDLED_FONTS
     void ActivateBundledFonts();
     nsCString mBundledFontsPath;
@@ -249,6 +254,9 @@ protected:
     // caching generic/lang ==> font family
     nsRefPtrHashtable<nsCStringHashKey, gfxFontFamily> mGenericMappings;
 
+    nsCOMPtr<nsITimer> mCheckFontUpdatesTimer;
+    nsCountedRef<FcConfig> mLastConfig;
+
     static FT_Library sCairoFTLibrary;
 };