Thunderbird Browser association lost after installing FF 3.6 on Jaunty

Thunderbird 3 was working fine until the upgrade. Then clicking links in emails just stopped working. I click, nothing happens. Eventually I figured out that the easy way (or the only way) to change the dead browser association is to try the links without FF 3.6 open. When I did that, Thunderbird asked what it should use to open the link, then I got to point it to the right thing. Not sure why, since I verified the default browser setting already, and FF 3.6 was from the Launchpad repository, not a version I downloaded directly from Mozilla...