Fuzzy font rendering issue
This happens mostly on Facebook.
Usually when you scroll the text is not crisp but it changes now and then, see pic.
LCD text antialiasing in flags is on Default, same when disabled.
Doesn't happen in Chrome.
Doesn't seem to be related to HiDPI (same on my 4K monitor as well as my 1920x1200 one, both on 100% scale)
Using latest 1.6 stable build.
This is a more extreme example, it's like it's "fading", after a moment it goes back to regular but then it can be bad again: