Here are a few small settings for Firefox 2 and 3 that will make them work faster:

Type: about:config (no spaces) in the URL bar, and hit enter.
You’ll get a small alert and next step will be to click on the “I’ll be careful, I promise!”

Now on the image you’ll see above you need to right click with the mouse and then New -> Boolean

Example:

Now you’ll have the New Bolean Value, you should type this:
config.trim_on_minimize (again, no spaces - just as it is)

Example:

click OK, and chose TRUE.
Now restart Firefox (close it and re-open)

The result: saving tons of memory and will make the browser faster.

Example:

To this: