Just ran the activity monitor to see why my mini (512MB 1.5GHz 10.4.4) was running so slowly, and realised that the latest version of Firefox was taking up 1.2GB of virtual RAM!!!
Also, it's taking up anything between 40 and 60% CPU time right now, with just this window (no other tabs) open, and 260-odd MB of virtual RAM. I know the mini isn't the fastest on the block, but c'mon! This sounds way, way out of line.
Gonna give Opera a try now. Anyone else have any of these issues?