FF 7.0a2 (got Jul 24 from the Aurora channel) is less responsive than FF 3.6 was on my machine -- although I cannot be sure that the unresponsiveness is due to memory pressure rather than, e.g., insufficient parallelism of the UI relative to the part that executes Javascript.
I think you can help them in this -- they're starting to gather UI responsiveness metrics. If you're seeing especially bad UI lag, they'd probably like you to run those metrics to help them figure out what is going on.
Disabling hardware acceleration (it's in the General tab of the Advanced pref pane) seems to have solved the horrible problems I was having with Firefox 7. Thanks!
