Nice, i suggest an option wich shows the default out-of-the-box windows fonts, i think this could be more low profile

The motivation for the author of the webextension is good, but... it did not protect the browser user from the fact that ANY tracking company can easily deteсt that you are using the extension to bypass the reading of your real data. So you are already trying to hide from them and this is a huge fingerprint. Webextension code needs to be rewritten significantly in order to protect it from detection. Good luck to the author, but in this form, the extension only pays attention to tracking companies.

Creates a new value with every page view. Excellent!

According to Panopticlick, this actually made it worse - I was in a bracket where one in 5,000 browsers had my font set, with this extension one in 253,000 browsers had my font set. You can't change the false data it sends either, so you can't fit yourself into a more common font set.

There is a problem with notification. Desktop notification is disturbing. Better place is in the toolbar section.
Need option for staying on the same fingerprint until the tab is closed.

It works. Test it on webbrowsertools.com/font-fingerprint/

Works as described. Thanks you! :)