PermaTabs creates a set of tabs that open up every time you start your Firefox (this plug-in is for version 2.0). So you do not have to open and upload manually the web sites you usually open at your start up (news, blogs, quotations etc..) and revisit throughout your working day, since PermaTabs allows them to be open automatically. To create a PermaTabs is very easy: simply just right-click an open tab and select Permanent Tab. The tab will become yellow as default) and you will not be able to see its close "X" on the top right. To remove the PermaTab just right-click again.
It is useful for keeping URLs you use often, always one tab away. Also, useful for picking up articles where you left off during a previous session. However some users complain about its graphics, and namely because the distinction between permatabs and tabs is not so evident.
The main feature - at least for me - is that you will not risk to close your tabs unwillingly; something that, well I don't know about you, but happens to me very often...
Tiny Menu is another good extension for Firefox that enables you to reduce the size of your browser's menu bar by shrinking all menu items into just a single button and simply using a drop down to access to all the menu item. You can also choose to keep selected menu items directly on the toolbar and only compress the items you prefer to get rid of.
After installation, in order to set up Tiny Menu, go to Toolbars Customization (menu View) and drag one by one all the items from your Navigation Toolbar until this becomes empty. Once you are back to Firefox window, go again on Toolbars (menu View) and uncheck the Navigation Toolbar. Now you have gained much room on you screen!
Let me know if you found these two extensions useful!