--- a/uriloader/exthandler/nsExternalHelperAppService.cpp
+++ b/uriloader/exthandler/nsExternalHelperAppService.cpp
@@ -482,17 +482,17 @@ static const nsExtraMimeTypeEntry extraM
 #endif
 
     // Note: if you add new image types, please also update the list in
     // contentAreaUtils.js to match.
     {IMAGE_ART, "art", "ART Image"},
     {IMAGE_BMP, "bmp", "BMP Image"},
     {IMAGE_GIF, "gif", "GIF Image"},
     {IMAGE_ICO, "ico,cur", "ICO Image"},
-    {IMAGE_JPEG, "jpg,jpeg,jfif,pjpeg,pjp", "JPEG Image"},
+    {IMAGE_JPEG, "jpeg,jpg,jfif,pjpeg,pjp", "JPEG Image"},
     {IMAGE_PNG, "png", "PNG Image"},
     {IMAGE_APNG, "apng", "APNG Image"},
     {IMAGE_TIFF, "tiff,tif", "TIFF Image"},
     {IMAGE_XBM, "xbm", "XBM Image"},
     {IMAGE_SVG_XML, "svg", "Scalable Vector Graphics"},
     {IMAGE_WEBP, "webp", "WebP Image"},
     {IMAGE_AVIF, "avif", "AV1 Image File"},
 
@@ -523,19 +523,16 @@ static const nsExtraMimeTypeEntry extraM
     {AUDIO_WAV, "wav", "Waveform Audio"},
     {VIDEO_3GPP, "3gpp,3gp", "3GPP Video"},
     {VIDEO_3GPP2, "3g2", "3GPP2 Video"},
     {AUDIO_AAC, "aac", "AAC Audio"},
     {AUDIO_FLAC, "flac", "FLAC Audio"},
     {AUDIO_MIDI, "mid", "Standard MIDI Audio"},
     {APPLICATION_WASM, "wasm", "WebAssembly Module"}};
 
-static const nsDefaultMimeTypeEntry sForbiddenPrimaryExtensions[] = {
-    {IMAGE_JPEG, "jfif"}};
-
 /**
  * File extensions for which decoding should be disabled.
  * NOTE: These MUST be lower-case and ASCII.
  */
 static const nsDefaultMimeTypeEntry nonDecodableExtensions[] = {
     {APPLICATION_GZIP, "gz"},
     {APPLICATION_GZIP, "tgz"},
     {APPLICATION_ZIP, "zip"},
@@ -2629,47 +2626,36 @@ NS_IMETHODIMP nsExternalHelperAppService
   if (!found && !aFileExt.IsEmpty()) {
     // XXXzpao This should probably be localized
     nsAutoCString desc(aFileExt);
     desc.AppendLiteral(" File");
     (*_retval)->SetDescription(NS_ConvertASCIItoUTF16(desc));
     LOG(("Falling back to 'File' file description\n"));
   }
 
-  // Sometimes, OSes give us bad data. We have a set of forbidden extensions
-  // for some MIME types. If the primary extension is forbidden,
-  // overwrite it with a known-good one. See bug 1571247 for context.
-  nsAutoCString primaryExtension;
-  (*_retval)->GetPrimaryExtension(primaryExtension);
-  if (!primaryExtension.LowerCaseEqualsASCII(
-          PromiseFlatCString(aFileExt).get())) {
-    if (MaybeReplacePrimaryExtension(primaryExtension, *_retval)) {
-      (*_retval)->GetPrimaryExtension(primaryExtension);
-    }
-  }
-
   // Finally, check if we got a file extension and if yes, if it is an
   // extension on the mimeinfo, in which case we want it to be the primary one
   if (!aFileExt.IsEmpty()) {
     bool matches = false;
     (*_retval)->ExtensionExists(aFileExt, &matches);
     LOG(("Extension '%s' matches mime info: %i\n",
          PromiseFlatCString(aFileExt).get(), matches));
     if (matches) {
       nsAutoCString fileExt;
       ToLowerCase(aFileExt, fileExt);
       (*_retval)->SetPrimaryExtension(fileExt);
-      primaryExtension = fileExt;
     }
   }
 
   // Overwrite with a generic description if the primary extension for the
   // type is in our list; these are file formats supported by Firefox and
   // we don't want other brands positioning themselves as the sole viewer
   // for a system.
+  nsAutoCString primaryExtension;
+  rv = (*_retval)->GetPrimaryExtension(primaryExtension);
   if (NS_SUCCEEDED(rv)) {
     for (const char* ext : descriptionOverwriteExtensions) {
       if (primaryExtension.Equals(ext)) {
         nsCOMPtr<nsIStringBundleService> bundleService =
             do_GetService(NS_STRINGBUNDLE_CONTRACTID, &rv);
         NS_ENSURE_SUCCESS(rv, rv);
         nsCOMPtr<nsIStringBundle> unknownContentTypeBundle;
         rv = bundleService->CreateBundle(
@@ -2689,18 +2675,20 @@ NS_IMETHODIMP nsExternalHelperAppService
       }
     }
   }
 
   if (LOG_ENABLED()) {
     nsAutoCString type;
     (*_retval)->GetMIMEType(type);
 
+    nsAutoCString ext;
+    (*_retval)->GetPrimaryExtension(ext);
     LOG(("MIME Info Summary: Type '%s', Primary Ext '%s'\n", type.get(),
-         primaryExtension.get()));
+         ext.get()));
   }
 
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsExternalHelperAppService::GetTypeFromExtension(const nsACString& aFileExt,
                                                  nsACString& aContentType) {
@@ -2897,36 +2885,16 @@ nsresult nsExternalHelperAppService::Fil
 nsresult nsExternalHelperAppService::FillMIMEInfoForExtensionFromExtras(
     const nsACString& aExtension, nsIMIMEInfo* aMIMEInfo) {
   nsAutoCString type;
   bool found = GetTypeFromExtras(aExtension, type);
   if (!found) return NS_ERROR_NOT_AVAILABLE;
   return FillMIMEInfoForMimeTypeFromExtras(type, true, aMIMEInfo);
 }
 
-bool nsExternalHelperAppService::MaybeReplacePrimaryExtension(
-    const nsACString& aPrimaryExtension, nsIMIMEInfo* aMIMEInfo) {
-  for (const auto& entry : sForbiddenPrimaryExtensions) {
-    if (aPrimaryExtension.LowerCaseEqualsASCII(entry.mFileExtension)) {
-      nsDependentCString mime(entry.mMimeType);
-      for (const auto& extraEntry : extraMimeEntries) {
-        if (mime.LowerCaseEqualsASCII(extraEntry.mMimeType)) {
-          nsDependentCString goodExts(extraEntry.mFileExtensions);
-          int32_t commaPos = goodExts.FindChar(',');
-          commaPos = commaPos == kNotFound ? goodExts.Length() : commaPos;
-          auto goodExt = Substring(goodExts, 0, commaPos);
-          aMIMEInfo->SetPrimaryExtension(goodExt);
-          return true;
-        }
-      }
-    }
-  }
-  return false;
-}
-
 bool nsExternalHelperAppService::GetTypeFromExtras(const nsACString& aExtension,
                                                    nsACString& aMIMEType) {
   NS_ASSERTION(!aExtension.IsEmpty(), "Empty aExtension parameter!");
 
   // Look for default entry with matching extension.
   nsDependentCString::const_iterator start, end, iter;
   int32_t numEntries = ArrayLength(extraMimeEntries);
   for (int32_t index = 0; index < numEntries; index++) {

--- a/uriloader/exthandler/nsExternalHelperAppService.h
+++ b/uriloader/exthandler/nsExternalHelperAppService.h
@@ -139,24 +139,16 @@ class nsExternalHelperAppService : publi
    * Does not change the MIME Type of the MIME Info.
    *
    * @see FillMIMEInfoForMimeTypeFromExtras
    */
   nsresult FillMIMEInfoForExtensionFromExtras(const nsACString& aExtension,
                                               nsIMIMEInfo* aMIMEInfo);
 
   /**
-   * Replace the primary extension of the mimeinfo object if it's in our
-   * list of forbidden extensions. This fixes up broken information
-   * provided to us by the OS.
-   */
-  bool MaybeReplacePrimaryExtension(const nsACString& aPrimaryExtension,
-                                    nsIMIMEInfo* aMIMEInfo);
-
-  /**
    * Searches the "extra" array for a MIME type, and gets its extension.
    * @param aExtension The extension to search for
    * @param aMIMEType [out] The found MIME type.
    * @return true if the extension was found, false otherwise.
    */
   bool GetTypeFromExtras(const nsACString& aExtension, nsACString& aMIMEType);
 
   /**