(In reply to comment #0)

P.S. We don't have an "image scaler" bugzilla component?

That's bug 41371.

(In reply to comment #0)
I can not see anything wrong with the image and it's thumbnail.
(There is some #fefefe-white as background in the source gif file. If this is the problem, I could easily fix that for you)

(In reply to comment #2)

(In reply to comment #0)
I can not see anything wrong with the image and it's thumbnail.
(There is some #fefefe-white as background in the source gif file. If this is
the problem, I could easily fix that for you)

I'm talking about those #f6f9fe pixels.

More precisely, those #fefefe are darkened into #f6f9fe, and lose a clear boundary.

This seems to be an upstream bug of imagemagick's convert command line tool. (I could reproduce similar results). You may file a bug at http://www.imagemagick.org/discourse-server/viewforum.php?f=3

Reopen if needed, images look alright now.