Rated 4 out of 5 stars

Wonderful add-on, however it breaks somehow the new functionality of FF13 so I had to disable it.

For more, please see

[addendum, 21/06]
Don't know how to add my reply to onemen so I use this way:
Thank you very much for your prompt reply!
I've done what you suggested and it seems to be working.
Switching this nice add-on on!

This review is for a previous version of the add-on ( 

Starting with Firefox 12, Tabmix default for Events/New Tabs > "Load on new tabs" and Events/Tab Closing > "When I close last tab replace it with" options changed to New Tab Page.
When you update Firefox to v.12, it resets Tabmix option to New Tab Page and you have to make your selection again.
You have few options if you had the Blank Page option selected previously:
use the New Tab Page for new tabs.
use the New Tab Page but disable it by clicking on the button on the upper right corner,
this will turn the New Tab Page into blank page for new tabs.
(or setting browser.newtabpage.enabled to false)
set Tabmix to load Blank Page.
set Tabmix to load New Tab Page and set the address to about:blank.