Created attachment 8623508 [details] Nightly screenshot (build 20150616030201) Current nightly (build 20150616030201) seems to use wrong fonts on some websites. You can see screenshots for compare - one with 20150616030201 and one with Firefox 38.0 (20150511103818). Both on latest Linux Mint. Also on with clean profile I see serif font used in UI (menu button), but sans-serif with used profile.
This might occur few days earlier, I have updated Nightly about a week ago and than today.
Seems OK again (build 20150624080416).