Firefox with Bing
 

This doesn't make sense to me. Not that it really matters, but I ran across the link to download FF with Bing as default search engine, I assume.

http://www.firefoxwithbing.com/

Then I get this message:
I wonder what difference it makes to MS not to include it for Linux???

Probably got some Windows only addon(they love a bit of non-portable code :) ), if it was just a default search engine it'd work OK (There's quite a few Win-only add-ons). However if I do research for work from my Debian PC at home, MS are keen to tell me that I'm using the "wrong" OS, esp. if I want to download something.

If addon is implemented as dll, it won't run on Linux, obviously.