Noel, one of the sys admins here at Feedster, just let me know this:
If you minimize Firefox, it will (automagically) reclaim memory that it's no longer using.
Apparently this is a workaround for the Firefox bug where it doesn't reclaim memory for tabs that you've closed (a long time FireFox / Mozilla bug I've blogged about in the past). Now when Noel told me this, I immediately tried it and saw my memory usage go from 153 megs* to 52 megs. Awesome. Thanks Noel. (Oh and this works in Thunderbird also so I strongly recommend minimizing your Firefox and Thunderbird windows every few hours).
* Yes I'm a Tabaholic. I'm currently searching for a support group on this. Please contact me if you have suggestions.
Picture of a Tabaholic
(That's like 25 tabs in one browser window and 5 browser windows open total; I do have issues)