The copy & paste bug has been present for years in FF - it seems to be pretty random, but most people have had 'success' reproducing it consistently by opening one FF instance, copying something (e.g. a URL) from it then opening another and pasting into that. It doesn't always happen, but usually does and, even more annoying, if you then type into anything (Google, a form etc etc) that requires an apostrophe, it opens the 'Find' dialog. You're then unable to type an apostropher until you completely close FF (and I mean from Explorer - closing it by shutting the browser window down doesn't work).
It has been documented ad infintum in newsgroups and on Bugzilla - every time FF release a new version they proclaim its fixed... but it isn't!
http://neosmart.net/blog/archives/141
http://www.quartertothree.com/game-talk/showthread.php?p=751664