Index: firefox-78.0.2/dom/media/platforms/ffmpeg/FFmpegRuntimeLinker.cpp
===================================================================
--- firefox-78.0.2.orig/dom/media/platforms/ffmpeg/FFmpegRuntimeLinker.cpp
+++ firefox-78.0.2/dom/media/platforms/ffmpeg/FFmpegRuntimeLinker.cpp
@@ -30,6 +30,7 @@ static FFmpegLibWrapper sLibAV;
 static const char* sLibs[] = {
 // clang-format off
 #if defined(XP_DARWIN)
+  "libavcodec.58.91.dylib",
   "libavcodec.58.dylib",
   "libavcodec.57.dylib",
   "libavcodec.56.dylib",
@@ -37,6 +38,7 @@ static const char* sLibs[] = {
   "libavcodec.54.dylib",
   "libavcodec.53.dylib",
 #else
+  "libavcodec.so.58.91",
   "libavcodec.so.58",
   "libavcodec-ffmpeg.so.58",
   "libavcodec-ffmpeg.so.57",