Comment 90 for bug 239952

(In reply to comment #28)
> Hello guys,
>
> I'm using Fedora 12 and had this bug opening RAR, ZIP, etc files from firefox.
> I solved it by choosing (usr/bin/file roller) instead of Archive Manager as
> default.
>
> Does this make sense?
That is a workaround.

(In reply to comment #29)
> This seems to be fixed in a recent trunk build for me:
> Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.3a5pre) Gecko/20100428
> Ubuntu/10.04 (lucid) Minefield/3.7a5pre

It happens on some systems with certain mime types provided by web server.
It may happen with some files, and may not happen with some other files, even if the file ext are same.

See also Bug 464443.