Comment 164 for bug 512615

I suspect a lot of you upgraded. I've had this before in previous upgrade/downgrade issues where Firefox and Thunderbird skitz out and show horrible fonts. Thankfully the fix is stupidly simple:

sudo fc-cache -fv

Then kill off firefox/tbird and re-launch them. You'll have crisp, dainty fonts.

It always takes me about 12 hours to find that out each time I break my fonts. I should alias it.