hi, thanks for reporting this. we are currently looking into this issue in https://bugzilla.mozilla.org/show_bug.cgi?id=1435472

so far it appears to be an issue that only affects users who have turned off cleartype font rendering within their windows settings. so a workaround for the moment would either be to turn cleartype back on or disabling hardware acceleration in firefox as you've discovered: Firefox's performance settings

i'm checking the functionality with cleartype enabled. I'll report you some updates

Same problem.

For what it's worth, the problem does not occur for me when running Firefox with add-ons disabled. I'm guessing it is a compatibility problem with one of the default add-ons since I don't have any additional add-ons installed.

@tx350z, hi if you're running firefox in safemode, hardware acceleration is disabled as well - the issue won't be due to one of your addons