Edited as this doesn't apply to your 115.4.0 ESR Firefox version. In Firefox 119 Fingerprinting protection has been added to Enhanced Tracking Protection in Strict/Custom mode (Suspected fingerprinters) what affects accessing local fonts. To include user installed fonts, modify this pref on the the about:config page:

• about:config => privacy.fingerprintingProtection.overrides => -FontVisibilityBaseSystem,-FontVisibilityLangPack

Issues with a weird looking font or missing glyphs can be caused by a problem with a specific font and you need to identify this font and fix this. You may find that it can be resolved by finding and removing duplicate fonts installed in the local ~/Library/Fonts folder, that are conflicting with standard system fonts.

You can check in Font Book for font issues like corrupted and duplicate fonts. Note that you should be careful about disabling "Allow pages to choose their own fonts, instead of your selections above" as this will cause issues with iconic fonts used by webpages to display small icons (you may see text labels instead of icons).

Go to about:config and try changing gfx.e10s.font-list.shared to false then restart the browser.