3. Scrolling performance:
There are also some scrolling techniques developed by HCI academics. Orthozoom is an example were horizontal movements on a vertical scrollbar control the zoom of the page: 
Back and Forward
Why is it that there is a delay in going back and forward and there is no delay in switching tabs?
I personally would not like Firefox to add itself to the startup programs. The most annoying thing about Adobe and Java's Runtime environment is that they do that.
Also, please review the discussions of the splash screen when Firefox was first being developed - I imagine they are still relevant today.
Netscape implemented a feature (which was off by default in mozilla) called QuickLaunch.
My memories were that: it did the launch into taskbar for Windows-only. It was really buggy, because the designers did not understand larger application-session issues (like cookies, profile switching, and mailnews). Doing this on FF should be easier because it is browser-only, and the architecture is more mature (in those days, we couldn't switch-profile in a session, the way Seamonkey does now...)
Even if you don't use the code, you could probably get a lot of useful design lessons and test cases...