I fill out a lot of complicated forms and edit a lot of Wiki pages. As much as I love Firefox, there are times that it locks up or crashes, which makes me lose all that work. I just discovered Lazarus, which is a Firefox plugin that stores all your form data as you type. Now, even if I accidentally close a window/tab, I can only lose a few seconds of work!
Lazarus stores the data in an SQLite file-based database in your profile directory, so it persists even reboots. It even has the option to store the data encrypted and password-protected, for you privacy nuts out there (/me raises hand). It’s completely unobtrusive, and does exactly what it says it does. Give it a try!