My Firefox hangs up when installing this extension. When I killed its process, it prevented my Firefox from starting somehow, all my tabs from the last session showed up, but none of them could actually load the page.

This behaviour was consistent: everything worked when I restarted Firefox in safe mode, then restarted as usual (no tabs loaded), then tried to disable the extension and restart (no tabs loaded, as the extension also blocked me from disabling it) and finally uninstalled it (everything worked).