I recently upgraded to FireFox 8 across the board on my computers. I’m running my gmail browser client off on my macbook and noticed that I was suddenly unable to view the contents of my emails when I clicked on them. Additionally perplexing was the fact that I could no longer send a chat message to anyone on my buddylist as the text field wouldn’t come into focus.

After testing in Chrome and finding gmail working I did a quick google and discovered this fix:

I solved my problem by Updating all subscriptions for AdBlock Plus Go to FireFox upper left
Add-Ons
Extensions
AdBock Plus Options
Filters
Update all subscriptions
[sic]
Source

I ran the AdBlock Plus subscription update and all my issues are gone. Happy emailing everyone! Let me know if this fix works for you as well.