I notice that when I reply to emails in Thunderbird on Fedora 11, and write more than a screenful of text, and then attempt to select a block of text, the scrolling speed can be uncontrollably fast. I can't stop the scrolling at the line that I want. I can't remember if this is also true when I compose a new email.
rpm -q thunderbird thunderbird-3.0-2.1.beta2.fc11.x86_64
Bob