First, to get the add-ons, you need to start Firefox, then go: tools -> add-ons
From the add-on window (which I have resized to full screen height), click on the “get add-ons” button, then enter the add-on name in the “search all add-ons” box.
- Tab Mix Plus
is an excellent replacement for “Tab Kit” (which is no longer compatible with FF3.6, and doesn’t seem to be updated any more). Tab Mix Plus has a huge set of configurable items, some of which replace a handful of other add-ons that I once used. I’ll be providing a review, and some configuration hints in a later post. - Adblock Plus
blocks annoying advertising. Just remember that some websites rely on advertising to survive… so if you use Adblock Plus, you should feel a certain level of guilt… but not too much 
- Close Tab By Double Click. This add-on can be removed, as the same functionality is provided by “tab mix plus”.
- Flashblock
blocks flash objects, yet lets you re-enable the flash objects with just a click. Great for blocking ads that Adblock Plus cannot block. Also good for making a “busy” website look easier on the eyes. - Menu Editor.
I’ve only used this to change the right-click on a link action to: popup a menu that has the option: “Open Link in New Tab” option at the top of the menu. - QuickDrag: when you highlight a few words on a page, then drag the words a few pixels away, a new tab opens with the search results on those works (ie no need to copy and paste them into google). If you highlight and drag a url (eg: computer-aid.com.au ), then that url is opened in a new tab.
- Remove New Tab Button. This add-on can be removed, as the same functionality is provided by “tab mix plus”.
- SearchStatus
will display some ranking information about each site you visit. Once installed, I “move” it to the menu bar (at the top of the window). By right-clicking on the “q” logo, I select “highlight nofollow links” so all nofollow links show up as pink. I also enable pagerank, alexa, compete, mozrank. - Split Browser
works well on widescreen monitors. You can view 2 websites side-by-side, and I often enable the “sychronously scroll” option when comparing 2 versions of the same website. - Tab History Menu . I find I don’t use this add-on much.
- Tab Kit. This add-on can be removed, as the same functionality is provided by “tab mix plus”.
- TabRenamizer. This add-on can be removed, as the same functionality is provided by “tab mix plus”
- Undo Closed Tabs Button. This add-on can be removed, as the same functionality is provided by “tab mix plus”.
