This Firefox plugin is very handy. It stores and restores all information in your browser if it crashes or closes; including text-fields, history, and tab positions.
(The only drawback is if you have an ST item that you had submitted; it will re-submit the item when firefox restarts. I've gotten around this by temporarily renumbering www.math to localhost in /etc/hosts in the rare occasion that firefox crashes...)
Another feature is "snapback tabs and windows" which are a list of tabs/windows that I've closed. They can be reopened, with their history preserved. I use this feature at least once a day, when I close a tab and realize I needed it again.
-- DanielAllen - 12 Jan 2006
Note that Firefox 2.0 adds most of this functionality.
-- MikePatterson - 11 November 2006