For me the problem was only when firefox was running in retina mode. Going into Applications > Firefox > Right Click Get Info > Check "Open in Low Resolution"
The problem was fixed, but all the text looks bad now.
That's interesting. That fix seems unreasonable for me considering I already have difficulty reading on screens. But that's at least a point to look for later on in the release notes.
The problem was fixed, but all the text looks bad now.