If you love the Pin Tab feature in Chromium and Google Chrome browsers that crops tabs down to favicon-size, so you gain more tab bar space and would like to give it a try in Firefox, then grab the App Tabs Firefox extension. Pinning tabs doesn’t mean holding them down to a fix position, pinned-tabs can still be shuffled within the pinned tab area.
After installing the add-on, right-click on tabs and select “App Tab” to pin them on the left side of your tab bar. You can also use keyboard shortcuts to pin tabs; Shift+Click, Double-click, Click+click and Alt+click are the possible options you can setup in “App Tab Options” dialog. Dragging tabs over into the pinned area also gives the desired effect. Naturally to undo pinned-tabs drag them out of the pinned area or use keyboard shortcuts you applied to pin them.
Given that Pinning tabs is going to be an in-built feature in Firefox 4, why not start getting used to it. App Tabs is a free download for all platforms (Windows, Linux and Mac). It works with Firefox 3.5 and newer versions. App Tab is an experimental add-on, it might not work with certain Firefox extensions and themes like Omnibar Extension.