I have also been looking for this "phenomenon" on and off, online, but could never find much information on it. It's really weird! It doesn't just happen with Firefox, but with all the other browsers as well –*Safari, Chrome, Opera.
I have an iMac, as well as a MacBookPro. Both are displaying these weird Helvetica fonts for about 2 years now, and it's increasingly infuriating as I'm getting it more and more on a lot of the websites.
I can't trash my Helvetica fonts as I'm a graphic designer. I need these fonts...
Can anyone recommend any solutions?
It's really strange that i can't google a solution... for the last 2 years I might add.