Print all the tabs!
The Firefox extension, Universal Print, provides Firefox with four printing modes: print this tab, print all tabs, print select tabs or print preview. These are definitely options I wish I had with the default Firefox installation. It is nice to know I can now print multiple tabs without having to jump to each one to start the process over again, and again, and again.

Work with a lot of tabs? Then you have probably seen the All Tabs menu (the menu at the right of the tabs bar) a whole lot. This bar allows you to manipulate tabs – but there isn’t too much you can do by default. One add-on that changes that is called All Tabs Helper. It gives you much more functionality to this heavily used Firefox feature.
Is Firefox acting a little slow? There are several little tweaks and fixes you can do to speed the browser up or to change the behavior of the browser so things seem faster. One of these that many people don’t know about is the option to not load up tabs until they are selected. 
One thing that sort of bugs me about Firefox is there is no real way to tell the difference between your active tab and your non-active tabs, other than a slight change in the background color. The User Style, FF3+ Increase active tab minimum width, will allow you to increase the minimum width of the active tab to make it stand out a little more.
Need to customize how many tabs you see in your Firefox window? Custom Tab Width is a really neat add-on for Firefox that makes doing this task really easy. It lets you customize the minimum and maximum tab width. Once installed, you simply need to go into the options for the add-on itself and then set the min number for the minimum size in pixels and the max number as the maximum number of pixels.
Need a quick way to open up all the tabs you have open in Firefox? As you may have already noticed – Firefox 4 has a pretty nifty "Switch to Tab" function that allows you to switch to an open tab, rather than re-launching the same website twice. What if you could open up all the open tabs in the Awesome bar?
Would you rather have your tabs back at the bottom of the toolbars rather than the top? This is an easy enough thing to fix with just two clicks of the mouse.