I'm having the same problem in FF and IE. Sometimes it will keep loading after logging in or switching screens. Refreshing doesn't seem to help. I just wait a while then try logging in again. Clearing cache doesn't help.

FF is my main browser, but last winter FF would have a lot of graphical problems with FKG. I switched to IE for only FKG. The newest build of FF (quantum?) is now OK, but IE still seems faster.

For mobile, Puffin seems to be one of the few mobile browsers that still allows Adobe Flash, so I use that for FKG on my phone when I'm away from home.