[link|http://techpatterns.com/forums/about623.html|TechPatterns] has some tips and a link to a Mozillazine thread about it.
I suspect in my case it's related to at least a few things:
I have Session Manager and Crash Recovery in TabMixPlus enabled. They have to know what to restore after shutdown, so they must keep a current picture of the current tabs somewhere. Since many of my tabs auto-refresh whether I want them to or not (various newspapers, etc.), it seems reasonable that that's a big part of the increasing memory usage. (I would think the code would be smart enough to overwrite the previous tab cache though.)
I'm a big fan of TMP, SM and CR so I don't know if I'm willing to make the trade-off of turning off those features for a smaller footprint.
I'll have to check my settings for A:C and see if that makes a difference as well.
In short, FF may be working as designed when my combination of extensions and settings are used. :-/
HTH.
Cheers,
Scott.