I used to have the same problem. I really dont know the name of my browser cause im just using the default one. I think the way i got around it was by just clicking a random thread link and it turned out i was in fact logged in after all. Sounds stupid and simplistic perhaps but have you tried it?

Gifs on the other hand i have absolutely no idea about. Havent even thought about it. Been a while since i logged in from the phone to be honest.