Hey folks! So...I've been dealing with this issue for the past week, but haven't managed to find any solutions. I've been having issues with using Flash in Firefox...I'm essentially unable to watch anything on YouTube. I tried re-installing Flash, and while the .dmg file is still open, YouTube worked for a minute or two (but has stopped working since). I can watch YouTube using Chrome, however, so it seems it's a problem between Flash and Firefox.