Rated 4 out of 5 stars

bibbolo may have some other add-on causing a conflict. I use a number of add-ons (no other font ones), and Font Finder 1.2.3 (which was current at the time of the bibbolo review) works great. It also does things that the WebExtension version, Font Finder (revived) 0.1.8 does not. In particular, it has the extra context menu options "Adjust element's [...]", "Replace font (entire DOM)", and "Disable font (entire DOM)".

The WebExtension version claims it, too, has the "Any active element can have any piece of the font's options (such as color, size or family) adjusted inline" functionality, but this does not appear to be true. The only context menu item is "Inspect Font", and none of the fields in its popup are modifiable. I also checked the screenshots and the FAQ (which, BTW, uses the misspelling "Fond Finder" in multiple places), to no avail.

I'm giving this XUL version of the extension 4 stars rather than 5 due to two issues. One is that it didn't actually address the problem I installed it for. The description says "Information Captured: [...] Font family (including actual font being rendered!)", which I was expecting to help me debug the problem I was having on Linux with extremely messed-up scaled-bitmap, all-caps font substitutions (even when the exact TrueType font specified in the stylesheet was installed). Unfortunately it doesn't tell you the "actual font being rendered" — it just tells you the font that the web page *requests* to be rendered. I then learned about running Firefox with the environment variable FC_DEBUG=1, but its output didn't give me any useful information about the incorrect substitution. Luckily after a bunch more Googling, I was able to figure out that going to about:config and setting gfx.font_rendering.fontconfig.fontlist.enabled = false would cause Linux Firefox to go back to the old Cairo-based font rendering rather than the broken Firefox 44+ version.

The other issue with the add-on is that when you restart for the first time with it installed in a given profile, you get into an infinite loop of popups and new windows or tabs yelling at you to install the WebExtension version instead (despite it not replicating all the functionality of the XUL version). Until you get ahead of it and start hitting OK on the popups, it'll keep on spawning more copies of the popup and more new windows/tabs with the WebExtension version's addons.mozilla.org page loaded. The popups are also modal and won't allow interaction with the window they're related to until you hit OK on that window's popup (even trying to close the window is disabled). Finally, that popup actually gives the opposite advice that it means to: it says "Font Finder is moving to WebExtensions! Please give the WebExtension version a try and replace it with this XUL version." Well, yes, that's just what I've done — I tried the WebExtension version and have replaced it with this XUL version.