Slowed me down Rated 2 out of 5 stars
It works well enough, although I'd like to see both more browser functionality built-in (e.g., ability to use Diigo toolbar) and an easier way to choose between viewing in a TB tab vs a browser tab.
But before I disabled this add-on, TB was using over 100% of available CPU cycles. And boy! Was my computer running hot! I disabled the app, and now TB is mainly using about 25% of CPU cycles.
Similar problems have been reported for a similar app, WebApp Tabs: https://addons.mozilla.org/en-us/thunderbird/addon/webapp-tabs/.