Problem: I've downloaded Firefox 4 and now I am no longer able to save my tabs. How can I fix that?
Solution: By default this function has been disabled. To enable it, do the following:
1. In the address line, type in "about:config" (without quotation marks). Click on "I'll be careful, I promise!"
2. In the filter field, type in browser.showQuitWarning. This should filter out all other options
3. Double click on the option that is left in the list. The value should switch from "false" to "true".
4. Close about:config tab and it should work