I have noticed recently some performance issues with Firefox where flash player is involved. Notably at bbc iplayer, where from click to start playing, there is a noticeable delay (you see the working circle for 5-6 seconds).
Trouble is I can't replicate this 100%, but it's close. Some other parts of BBC too (but it's kind of user specific)
Other flash like at Youtube seem fine

I can confirm that Google Chrome is absolutely 100% fine. No issues.

Chromium is better than FF but it does sometimes have the stalling as the video play loads.

I'm wondering if we are seeing the start of worse things to come?