This week I’ve experienced a problem with Firefox after the updated they have been pushing. I was unable to cut, copy and paste from Firefox. I couldn’t copy URL’s, text from web pages or anything. I started Firefox in Safe Mode and the problem was gone. It appears that my StumbleUpon Add-on was causing the issue. Once I disabled it, the problem went away when I started Firefox in normal mode.
I have been regularly running into these problems with Firefox lately. I would blame the add-on developers, but other plug-ins have stopped working with each Firefox update. It’s starting to influence me to switch back to IE.
Disable all your add-on’s and restart ff then one by one re-able them and restart ff find out which one is causing the problem