Firefox 29 is brand new so expect some bugs. Seems like your issue continues, I would temporarly revert back to Firefox 28, and wait for a new update. Sorry to hear reinstalling didn't work. Firefox 28

Have you had trouble anywhere else then gmail?

Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache

Press the <Alt> or <F10> key to bring up the tool bar. Then; Tools > Options > Advanced > Network > Cached Web Content: Clear Now

and

• Remove Cookies

Press the <Alt> or <F10> key to bring up the tool bar. Then Tools > Options > Privacy.

Under History, select Firefox will Use Custom Settings. There is a button on the right side called Show Cookies.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode; Press the <Alt> or <F10> key to bring up the tool bar.. Then Tools > Options > Advanced > General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites and see if there is still a problem. Then restart.

Thanks it worked