Why does firefox download youtube as .webm

Hi all,



I have one of those firefox add ons, which has worked wonderfully for me. When a youtube video would play, I had three coloured balls that would spin around and with one click, I could select 'download, 'quickdownload', etc. Files would download as .avi or .mp3 or .mpeg



Now, when I choose download, FF downloads as a .webm file. Attempting to convert this to a .mp4 or .mpeg file is no easy.



Is there a way to have FF download using the old method? Or is there an easy way to convert from a .webm to .avi/mp4, etc...



Thanks

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