Safari issues are a very low priority as it's a very uncommon browser on Windows, and we don't make any Mac software.
What exact circumstances are you seeing slow scrolling under? I use FF 3.0.10 myself and haven't seen any issue with wheel scroling or autoscroll.
firefox always scrolls slow when many messages or threads are displayed. And it's happening on Mac AND Windows for me.
And your site is the ONLY site that slows down that horribly.
I have several addons installed, among them AdBlock, RePagination (or occasionally AutoPager), Foxmarks. Disabling them has no effect.
The slowdown occurs even after the page completely loaded.
When I scroll down with the Pgdwn key, there's a tiny but noticable lag when FF tries to paint the message entries under XP. Lag is even worse under Mac, but the Mac has a slower CPU anyway.
I ran some tests and the only way to get fast speed under FF was to disable stylesheets. Of course it looks like shit that way.
And regarding Safari, maybe this gives you a clue: When trying to drag the link-dialog, indead of dragging the window it drags a piece of text which even creates a link.
Text: "javascript:;". href the same.
And to add another browser: Google Chrome doesn't work with quote buttons