You are the man for making this. Top kudos to you friend.
I had to use this because Google forces HTML5 on Youtube now, and low and behold, forced standardization has issues, I wasn't able to view video at anything other then 360p, thanks to this add-on, I can view everything again.
I would like to point out to other reviewers that its not Firefox thats forcing HTML5, its Google.
Firefox is FOSS meaning, while its developer friendly, it lets you use what YOU want to use (be it flash, HTML5, Silver light, etc) I recently switched from Chrome to Firefox, and I have to say, I like it much more considering Chrome and Google were making HTML standard on everything, and were disabling silverlight (which is a plug-in many thing rely on). So up Google, and thank you based Mozilla.