Thanks for the info. I hope it solves the problem - it should. When I opened Mail and clicked on default browser, a list of maybe 100 items popped up, most having nothing to do with browsers (private monitor exe.app, etc). All of them had "(my boot camp)" at the end, EXCEPT Thunderbird. SeaMonkey(my boot camp) was the only SeaMonkey title in the list.
Obviously, the list came from my boot camp partition.
Finally, I scrolled all the way to the bottom and saw "select", which allowed me to browse my computer's Application files and select the right SeaMonkey.
I think Lion has a lot of bugs.