The final icons should be 32x32px gifs, animated or non-animated.
Can it be a still PNG8 (256-color palettized PNG) or an animated APNG8
(0) instead, so that attribution metadata
(1) could properly be retained?
Note that I release my artworks --including icons-- under
copyleft terms; and in such case, proper metadata fields are essential.
And if these are allowed, is partial transparency allowed too?
(3) Or submissions must use 1-bit alpha channel like traditional GIF files?
(0) You know, Mozilla's backward-compatible animated variant of PNG. (And did you know that animated version of GIF also came from Netscape/Mozilla too?)
(1) GIF only has a
single freeform metadata text field with no meaning associated to it; unlike PNG, which
has Title, Artist, Copyright, Description, among other things.
(2) Unlike GIF which uses a special "transparent" palette entry, PNG8 allows color in each palette entry to specify its own 8-bit alpha value.