I had this issue as well. Could not get any help in IRC or Matrix channels. Wasted time trying to work around it in fontconfig settings on Linux but the way that Firefox is choosing fonts now is absolutely bizarre.
I tried upgrading to 119 but fonts outside of Private Browsing were affected in that version.
There's a mention of something like this in the 118 release notes:
> The visibility of fonts to websites has been restricted to system fonts and language pack fonts to mitigate font fingerprinting in Private Browsing windows.
However, this describes a behaviour opposite of what is happening. My font settings in Firefox and from my system are not being used.
Also, I don't care about the case for fingerprinting -- this is about as stupid as Firefox deciding that it only runs at 800x600 in order to mitigate fingerprinting. Even in 119 I had a unique browser fingerprint in Private Mode. So it doesn't matter and I don't care. If I cared, I would use the Tor Browser.
I've since downgraded to 111 and I might revisit this later when I have more time and patience to waste.
