Every now and then a beloved piece of software acquires a new feature that sounds good on paper, but really breaks your workflow. This is the case with Firefox’s relatively new found ability to play directly linked MP4 files in the browser without a plugin. Nothing wrong with that, I just prefer to download such files – usually HD movie trailers – using DownThemAll and watch them later using VLC.
So here’s how you revert to the old handling of MP4 files:
Enter about:config in the address bar
Click I’ll be careful, promise!
In the Search field, enter media.windows-media-foundation.enabled
Double-click the True in the media.windows-media-foundation.enabled result to change it to False