Comment 104 for bug 25830

comment 18 suggests that adding this enhancement would offer users "more power
than any other browser I've seen" - as if that's a reason not to do it. The
suggested alternative is "make the user do a bit more work" - so the user is
protected from something "annoyingly incomprehensible" like a Handle As...
option, and instead only has to download the silly file, open a shell window and
rename the file to have a recognized extension, and go back to Moz and type in a
file: url for the new file in order to view it. And remember to remove the file
after.

That isn't any more comprehensible or less annoying to a novice user, and if I
had a novice user on a support line I'd much rather be able to say "hmm, dialog
asking what to do with application/x-pdf? Yeah, just pick Handle as
application/pdf, it'll be fine."

I actually see things served as application/x-pdf often enough that I have an
entry in MIME types for "Mislabeled Portable Document Format". :( And then
there's always the occasional html/text or txt/html or other wacky content type
where you see it and you know immediately what it was supposed to be but you
have to go run around the block in order to view it.

For UI, I'd suggest that Handle As... gives you a selection box to pick from any
of the types currently known to the browser, ideally with more common ones and
closest fuzzy matches to the served content type toward the top. With a tip for
the Handle As button saying something like "Use if you think you know what type
this document really is" I don't think it really has to be incomprehensible.