Firefox is a great browser, but it costs a lot in memory usage. It's not uncommon to see 50,000 KB of memory in use. While that can't be fixed completely, here's a way to cut down on memory usage when it's minimized:

1. Open a new tab.

2. Enter about:config into the Address Bar.

3. RIGHT-Click in any empty space. Create a New Boolean.

4. Enter config.trim_on_minimize as the Boolean's name.

5. SET it to true.

Close and restart Firefox. You'll notice a sharp decrease in memory usage:

MAXIMIZED:



Minimized:

I did this with Firefox 2 but I didn't notice a big difference.

However, Firefox 3 has been gobbling up a lot of memory and with this Config Edit, it's gone from 50k at startup down to 12k.
It also purge its memory every TIME you minimize. (right down to 5K)

Wonderful!