Rated 5 out of 5 stars

Tree Style Tab more effectively used in conjunction with other add-ons, such as All-in-One Sidebar, Multiple Tab Handler, TabGroups Manager, Session Manager, Tab Mix Plus, Tab Counter, etc.
In this case, you can organize your work in Firefox is much better.
The latest versions of Firefox (from version 8) by default has the option "Don't load tabs until selected". With the option enabled, after the startup of the browser, all tabs are not refreshed automatically, only one current tab is refreshed, the other tabs are not refreshed and are not loaded into memory.
Right now I have 474 opened tabs in Firefox, Windows Task Manager shows that Firefox consumes 733 MB of memory. At my home computer opened more than 3000 (!) tabs (under Debian Linux OS), and the browser consumes around 2 - 2.5 GB of memory.
With the above add-ons you can be easily and effectively work with a lot of tabs. As long as you do not select any of tabs, they do not consume memory. Now I don't use bookmarks, all sites, that I need, opened in my browser.
The performance of the Tree Style Tab is quite well.
Perhaps, Firefox is too slow, if before that was multiple upgrades of the Firefox version on the same user profile? You can try to create a new, clean profile.
After the implementation of the tabs animation function in Firefox (since version 19) Tree Style Tab has become somewhat buggy when you move the tabs, especially in the most recent versions of Firefox, in particular, in Aurora-version of Firefox.
I hope the author will fix it soon )
Otherwise, Tree Style Tab - just a wonderful add-on.
Really, must have )

This review is for a previous version of the add-on (0.14.2013040601.1-signed).