This extension is good, but has the following drawbacks:
1、No dark mode.
2、No multi-language support.
3、As per the instructions provided by the author seven years ago (ReFont menu > Show More > Site font > Default font), I did not see "whitelisted".

You can apply niche font types that are installed on your local computer, by adding correct full names of them into the library.

Please stay on Up to dated.

Claims you can import font from your computer, but has no such option

EDIT:

It turns out you can, but it's really tricky due to the UI

Great :D Thanks https://addons.vaultpit.io/fr/firefox/user/13230872/

Finally I can change a few sites that use material design fonts with stupid arrows and symbols without changing my global settings to prevent the horrible antialiased fonts most use from ruining my eyesight! Thank you sir!

EXCELLENT!
Amazing to transform game server pages, that include config files: Now I can edit code/script with monospace font!

TUTORIAL?
1) Click 3 times the bar icon to refresh the addon; If it doesn't work = keeps "loading", its because that site is forcing its own font types, ex: jsonlint dot com / umod dot org (developer should explain this to avoid 1 stars, not his fault)
To change this behavior, go to Firefox "Options" > "Fonts and Colors" > "Advanced" > On the popup "Fonts", uncheck "Allow pages to choose their own fonts, instead of your selections above". That is it, now it will work. But remember that some sites like Firefox/Mozilla will still block changes.

1) Ok, lets start again: Click 3 times the bar icon to refresh the addon (turn on, off, on)

2) Click the greyed out option "Show more"

3) Choose "Site Font" to change ALL pages on that site domain OR "Page Font" on only remember changing the current page. Like Tod Howard said, it just works!

It applies one choosen font to EVERY Website, i love it!

People seem to be complaining about the 'loading' bug. A simple way to fix it seems to be just to close and re-open the add-on thing, that seems to work for me.

This extension is great and it allows us to choose how we want to view the web. It works perfectly with Firefox's capability to customise the cleartype settings. However, the load time is quite inconsistent with the latest Firefox. I wonder if there will be any update soon to address the load time issue? Thanks again for this great add-on.

What a fantastic addon thank you :)

Great but seems to have broken.

Great addon. Very useful and easy to use. Only annoying thing is none of your system fonts like Calibri, Segoe UI, Trebuchet MS, Tahoma, etc. show up in the list of fonts so you have to manually type them out to add them but I'm not sure if the filename in the font folder is the correct name or the font names in Firefox options. I wish you could simply scan the font folder to add the fonts or at the very least give some indication you typed the right name.

But it's still an excellent addon. I use this with Zoom Page WE (to change the font size) and it works beautifully.

Edit: I just noticed when you type out the correct name in the search box the name will change to that font style. So there is a visual indicator to let you know it's the right name.

Amazing

nice! gives them internets a uniform appearance and easy to set a site to use its own font in 2 clicks

the css amuses me too :)

well done

This does exactly what I wanted. It replaced the ugly Roboto font in YouTube with Consolas.