It's been a while, but I've had enough of it.
I am using Firefox on Nexus 4, and it seems that I can't vote from my phone when browsing in "full site" mode. The mobile site allows voting, the SE application allows voting. But the full site doesn't.
All the other functions work fine (flagging, voting to close, even requesting the +/- vote count).
(I tried clearing the cache, several times, and it didn't work.)