I think Mario is talking about the runtime memory usage. I mean, disk space is cheap these days...

It's possible to tweak Firefox to stop caching pages, multi-pipeline downloads etc. and there's this nifty addition to the config that has Firefox strip down to sometimes < 10MB of memory usage when minimized. If you have a decent amount of runtime memory for Firefox saaay 30+ MB this could be the way to go.

It's because Opera has so many more features to begin with
Wow, I didn't know it has a built-in XHTML debugger, download accelerator, music player, FTP client, GMail virtual drive client, HTTP header viewer, world map plotter... Opera must be waay more bloated than I thought!

You could try hack the Firefox source to make it cache stuff to disk or something, heh. Or refuse to cache certain stuff at all. It will probably save 80% on memory usage... and increase CPU/bandwidth usage by 5+X Well it's your choice. Can't you upgrade the RAM chip or something? Granted, notebook stuff ain't cheap, but this would seem to me a worthy investment if you're intent on extending the useful life of your computer as long as you can.