https://superuser.com/questions/267726/how-do-i-disable-font-smoothing-hinting-anti-aliasing-on-firefox-4

That old method of completely disabling hardware acceleration may adversely impact videos and maps, so I suggest saving that as a last resort. I've experimented with settings for Windows in past threads, but I somehow doubt that "ClearType" preferences even exist on Linux (or if they do, would they have any effect?). Still, you could take a look: https://support.mozilla.org/questions/1120385#answer-870910