Tabs are a pretty standard part of Firefox, but there are always users who want a little bit more from their software. Tabextensions was known variously as TBE3 and Tabbrowser Extensions, but with a new name and a major update, it looks considerably different to its predecessors.
In fact, Tabextensions isn't even a single Firefox add-on, it's a pack of 4 - Informational Tab, Multiple Tab Handler, Source Viewer Tab and Tree Style Tab. Each of the components has its own configuration options, which either means lots of great options, or too many irritating choices, depending on your point of view. The tabs themselves can be positioned to any side of the screen, and there are a number of skins and appearance options, although I have to say I wasn't very taken with any of them.
Apart from the individual configuration windows, you can also right click on the Tabextensions tab bar for a range of overall options. These range from standard tab behaviors, such as closing and reloading, to more advanced options, such as closing all tabs to the left or right, copying URLS, or saving a selection of tabs for later use. There are so many options, in fact, that it's hard to fit even a small percentage into this review.
Tab add-ons are ten a penny and whether or not you find them useful is a very personal decision. Tabextensions offers way more options than the average user will need, but if you want tight control of your tabs, and don't really care about their appearance, Tabextensions might well be for you.
If you like highly configurable tabs, Tabextensions is definitely the add-on for you!