“Tab Mix Plus (TMP) is a very popular extension for the Mozilla Firefox browser that enhances Firefox’s tab browsing capabilities. It includes such features as duplicating tabs, controlling tab focus, tab clicking options, undo closed tabs and windows, plus much more. It also includes a full-featured Session Manager with crash recovery that can save and restore combinations of opened tabs and windows.” – TMP Author Website
The above introduction will not be necessary for those of you already familiar with Tab Mix Plus, since you are like me looking for a version fully compatible with most recent release of Mozilla Firefox 3.6, well there is a version available which works for me without any problem in Firefox 3.6, hoping the same for you.
Click the following; it will open a new Firefox tab along with a warning whether to Allow installation from the said source or not, click Allow and a new Firefox dialogue will show up, just click Install there when it appears, restart Firefox and you are good to go. I am not hosting this version, it is directly from developer of Tab Mix Plus; “oneman”.
Fasterfox Lite 3.0.21 for Firefox 3.5.4
Mirror (uploaded by me): http://rapidshare.com/files/205568217/fasterfox_lite-3.0.21-fx.xpi
Size: 101 KB
Fasterfox & Fasterfox Lite for Firefox 3.5/3.5.7 – Latest (updated on 10-Feb-2010)
Fasterfox Lite: https://addons.mozilla.org/en-US/firefox/addon/9148
The last one was mentioned by Markoi in comments, with thanks to him. Simply visit any of the above, click “Let me install the experimental add-on” and let it do the magic for you =).