The problem hadn't reared its head particularly prominently in pre-release test versions, release manager Christian Legnitto said in a bug comment.
"Interesting that this doesn't show up in the top 300 crashes in 3.6.9pre or 3.5.12pre," he said. However, he pointed out in a follow-up remark, "Though this was a spike, the overall 'crashiness' of Firefox 3.6.x has not really increased at all. At about 1k [1,000] crashes a day, this crash is a drop in the bucket vs. active daily users."
"Because it is a crash on start-up that could prevent people from using Firefox entirely, we feel it was best to get a fix out quickly," he added.