Broken in 22.0a2 Rated 5 out of 5 stars
Not functioning. Keyboard shortcut not responding, UI button is hidden (and from Customise Toolbar list) and no entry shown in right-click menu.This review is for a previous version of the add-on (0.8.5). This user has a previous review of this add-on.
There was a bug in 0.9.1 which is fixed in 0.9.2. Due to that bug, I removed v0.9.1 and v0.8.5 (which you have now) didn't have support some tags recently required by addons to have to support (or alternatively opt-out) of private browsing.