When my mum installed Thunderbird 5, it would just crash at start every time.
Searching for the cause on crash-stat, quite quickly led me to see there was a lot of complaints of users with a similar experience, and then to bug 662634 and several other associated bugs. That bug generated several different backtraces that I believe were almost all in the top crashes for Thunderbird 5, from what I've seen in the bugs I think it was responsible for at least 3 of the top 5.
And whilst the fix (bug 660778) was checked in on the 11 of July, users had to wait until Thunderbird 6 for the fix which is a long time when your Thunderbird is completely broken.
I think you should consider checking the users having this problem and that left a description and their mail on stack-trace, and warn them they should download and install TB 6 that will probably fix it. I think the gesture would be appreciated.