What of you launch firefox from a console, it will display all the errors and such !
Could you please post this output for us. There might be usefull information in this log.
Hi, it seems its not flash the one lagging, its all of firefox, even typing this text is slow with or without a flash page loaded, I still dont know whats triggering the slowdown.
Hello !
What plugin and extension do you use?
Try to disable all your extension and enable them one by one, to see wich one is the one slowing things down.