diff --git a/layout/style/nsFontFaceLoader.cpp b/layout/style/nsFontFaceLoader.cpp
index d561b04cca3..eecd0518245 100644
--- a/layout/style/nsFontFaceLoader.cpp
+++ b/layout/style/nsFontFaceLoader.cpp
@@ -413,54 +413,39 @@ static PLDHashOperator DetachFontEntries(const nsAString& aKey,
   return PL_DHASH_NEXT;
 }
 
-static PLDHashOperator RemoveIfEmpty(const nsAString& aKey,
-                                     nsRefPtr<gfxMixedFontFamily>& aFamily,
-                                     void* aUserArg)
-{
-  return aFamily->GetFontList().Length() ? PL_DHASH_NEXT : PL_DHASH_REMOVE;
-}
-
 bool
 nsUserFontSet::UpdateRules(const nsTArray<nsFontFaceRuleContainer>& aRules)
 {
   bool modified = false;
 
-  // The @font-face rules that make up the user font set have changed,
-  // so we need to update the set. However, we want to preserve existing
-  // font entries wherever possible, so that we don't discard and then
-  // re-download resources in the (common) case where at least some of the
-  // same rules are still present.
+  // destroy any current loaders, as the entries they refer to
+  // may be about to get replaced
+  if (mLoaders.Count() > 0) {
+    modified = true; // trigger reflow so that any necessary downloads
+                        // will be reinitiated
+  }
+  mLoaders.EnumerateEntries(DestroyIterator, nullptr);
 
   nsTArray<FontFaceRuleRecord> oldRules;
   mRules.SwapElements(oldRules);
 
-  // Remove faces from the font family records; we need to re-insert them
-  // because we might end up with faces in a different order even if they're
-  // the same font entries as before. (The order can affect font selection
-  // where multiple faces match the requested style, perhaps with overlapping
-  // unicode-range coverage.)
+  // destroy the font family records; we need to re-create them
+  // because we might end up with faces in a different order,
+  // even if they're the same font entries as before
   mFontFamilies.Enumerate(DetachFontEntries, nullptr);
+  mFontFamilies.Clear();
 
   for (uint32_t i = 0, i_end = aRules.Length(); i < i_end; ++i) {
-    // Insert each rule into our list, migrating old font entries if possible
+    // insert each rule into our list, migrating old font entries if possible
     // rather than creating new ones; set  modified  to true if we detect
-    // that rule ordering has changed, or if a new entry is created.
+    // that rule ordering has changed, or if a new entry is created
     InsertRule(aRules[i].mRule, aRules[i].mSheetType, oldRules, modified);
   }
 
-  // Remove any residual families that have no font entries (i.e., they were
-  // not defined at all by the updated set of @font-face rules).
-  mFontFamilies.Enumerate(RemoveIfEmpty, nullptr);
-
-  // If any rules are left in the old list, note that the set has changed
-  // (even if the new set was built entirely by migrating old font entries).
+  // if any rules are left in the old list, note that the set has changed
   if (oldRules.Length() > 0) {
     modified = true;
-    // Any in-progress loaders for obsolete rules should be cancelled,
-    // as the resource being downloaded will no longer be required.
-    // We need to explicitly remove any loaders here, otherwise the loaders
-    // will keep their "orphaned" font entries alive until they complete,
-    // even after the oldRules array is deleted.
+    // any in-progress loaders for obsolete rules should be cancelled
     size_t count = oldRules.Length();
     for (size_t i = 0; i < count; ++i) {
       gfxFontEntry *fe = oldRules[i].mFontEntry;