It could be that Firefox kept running my machine out of memory. I’m going to be watching its memory usage closely to make sure on of the many plugins I use doesn’t have a memory leak. Additionally, I have never cleaned out my bookmarks. That means, every url I bookmarked since Firebird version 0.7 I still had. Also my history had every day’s usage remembered back through June. I deleted every bookmark (since those are all duplicated on Delicious anyway. And I cleared my history (which was a little disconcerting because I do go through that history regularly and pull things out that I need). Back to work.
You might want to create a new profile. And fx is a well-known memory hog. On my box, FX regularly stays over 120mb ram usage. I restart it a few times a day and try (but fail) to reduce my tabs to below 10.