I like UI of MicroB better, and the swirl-zoom is great of course. However, I like the tabs a lot in Fennec. And of course the more modern rendering/javascript engines.

I think Fennec uses way too much RAM and N900 simply doesn't have enough available memory to handle it much of the time. Just like everything else on N900, once you're hitting swap everything slows down like hell...

I wonder how it runs in Android? I thought android devices don't have swap. Perhaps the OS just has a smaller memory footprint.