Ok, here's the deal. After long use Firefox starts to lag like crazy with Flash. And... It doesn't seem to be a problem with Flash. It's more likely that the browser itself what is causing the issue. After I use Firefox for some time Flash starts lagging badly. BUT! This happens only if I have my Firefox window active. If I open the Task Manager on top of Firefox window, Flash stops lagging as if Harry Porter himself cast a spell with his magic stick making everything work like a charm. I made a small video showcasing the bug: https://www.dropbox.com/s/l2c5pbn1xwy58dc/12-11-2012%2019-07-15.avi - The bug still appears even in Safe Mode (all addons disabled). - With hardware acceleration disabled in Flash bug still remains. - With Chrome and other browsers everything works fine. - The bug will go away after restart - and then will start to appear after Firefox is in use for some time. - Normally it re-appears after I close my laptop's lid forcing it to go to sleep mode. After it wakes up - the bug is there. - There was no such a bug in the past - it started to appear as new Firefox versions were released - don't know the exact version but I assume it all started from version 14 or 15. Any thoughts?