I guess not. Hmm. Chris, I took a swing at downsizing an image, as the other thread icons appeared to be. I tried putting that .gif onto google drive, & linking that via the "Custom" icon field on New Thread. Looks like the board is doing it's best to deal with it. But I'm guessing Google Drive is just too weird as a repository.
Anyway, did I get the size & fiddly bits here (drive.google.com) right?
(Hey, I'm paying too much for a Photoshop license that I rarely use. Might as well get a bit of my $$$'s worth from it!!!)