Add-ons

Session Manager by Michael Kraft

Session Manager saves and restores the state of all or some windows - either when you want it or automatically at startup and after crashes. It can also automatically save the state of open windows individually.

Menu Wizard by Oleksandr

Customize menus : Helps removing, moving and renaming menus and menu items
Colorize important menu for ease of use! (use Style (CSS))
Change or disable any of used keyboard shortcuts
Support: Firefox, Thunderbird and SeaMonkey

Collector's Note remove all the junk from your context menus and color some most used items , saves great amount of time and pain :)

Add-ons Manager Context Menu by Zulkarnain K.

Add more items to Add-ons Manager context menu.