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Please see :

• https://addons.mozilla.org/firefox/addon/theme-font-size-changer/
• https://addons.mozilla.org/firefox/search/?platform=windows&q=font

Most all menus and Firefox interface can be changed bu userChrome ( This was in Firefox before there was a Google and they stole the name/engineers)

• https://www.howtogeek.com/334716/how-to-customize-firefoxs-user-interface-with-userchrome.css/
• https://www.userchrome.org/what-is-userchrome-css.html

As you can see it is make a folder, make a file in the folder, put the folder in the right place and copy/paste code, restart Firefox.

Please let us know if this solved your issue or if need further assistance.

https://addons.mozilla.org/firefox/addon/styl-us/

As noted in the complaint, the add-on suggested by PkShadow does not work with FF Quantum versions. Its feature for changing font/font size/font style of FF tabs does NOT work with any FF Quantum version! FF needs to add such accessibility feature to the Quantum itself! This has been going on since FF 57. Thank you.

Please Note, if you use the https://addons.mozilla.org/firefox/ in below 57 it will show you Extensions for below, same for above. Note : when you use the add-ons search page in Firefox 62 you get this result https://addons.mozilla.org/firefox/addon/theme-font-size-changer/

When you find one that will not work with your version the will be a LARGE RED Banner saying it will not work.

This Extension works for 57+