Open up: about:config?filter=keyword.enabled
Set it to false.
Now things like "bjafbsaofbdnaspolnas" will just end up at "http://www.bjafbsaofbdnaspolnas.com/".
The whole point of having separate bars is to clearly distinguish use, and to ensure data doesn't leak. This bothers me, too.
BTW, actually it seems that if I type `//foo` and `http://foo/` can't be resolved by DNS server/hosts file, Firefox does Google search, while Chrome tells that 'webpage is not available'.
Note also that some browsers want to fix http://foo to http://www.foo.com - for Firefox, see [1] and [2]
[1] about:config?filter=browser.fixup
[2] http://kb.mozillazine.org/Firefox_:_FAQs_:_About:config_Entr...
Do you mean after you press enter? I can't replicate your finding for words that are simply typed into the location bar.