This keeps happening to me as well on my brand new MBP.

I suspect it has something to do with Panorama/Tab Groups.

Most of the time after sleep FF won't respond, but when it finally does I usually switch to another Tab Group.

The zoom animation for Panorama will freeze halfway through & I'll have to force quit.

Funny thing is even with the Panorama animation frozen, I can still use the file menu & save my session with the Session Manager add-on.

It now appears that Firefox will hang at any time, not just after putting the MAC into sleep mode. You are able switch between tabs but not a lot else. I'll try disabling the add-ons.

I've found that disabling the Panorama animation has helped a lot.

http://techdows.com/2011/01/disable-panorama-or-tab-groups-animations.html

Haven't had FF freeze up all day, even after putting my MBP to sleep 2-3 times.

Too bad the animation was kinda nice.

Had the same problem (firefox and thunderbird hang after sleep) with 2011 MBP

Solved it by deleting the preference files - not sure if this step was necessary, consider taking backup copies first:

~/Library/Preferences/org.mozilla.firefox.plist

~/Library/Preferences/org.mozilla.thunderbird.plist

then, resetting firefox settings:

http://support.mozilla.com/en-US/kb/Basic%20Troubleshooting#w_6-reset-your-firefox-settings