I just installed it. So far, it does what it says it does, but I find that the rather large slider/button it displays over the page to be a problem. It obscures page content. It would be much better to make the Toolbar button a simple toggle. Maybe change color and/or shape when the page is locked? I have used other extensions that do this. Tabloc, for instance. Either that, or add options to make the button small or to move it.

"To dismiss the button, press the ESC button on the keyboard" — does not work in Mozilla Firefox 132.0b4 (64-bit) under Microsoft Windows 10.0.19045.5011. In addition, add-on is not FOSS, and after restarting the browser, all restrictions set by the extension are reset, and they have to be set again.