Whoa creepy, I actually just read an article saying exactly that in Utah, that if your boss thinks you're gay, you can be fired. I guess sh/e doesn't even have to prove it...
And I'd just like to add that, earlier this month was the first time in history that registered Democrats outnumbered registered Republicans in New Hampshire. 
Way off-topic here, but that's not only Utah. It's the vast majority of states.
The following states have laws forbidding firing on any basis of sexuality:
Minnesota
Rhode Island
New Mexico
California
District of Columbia
Illinois
Maine
Hawaii
New Jersey
Washington
Iowa
Oregon
Vermont
Colorado
And the following states have laws forbidding discrimination on the basis of sexual orientation, but not other aspects of sexuality (so not transgender people, for example):
Wisconsin
Massachusetts
Connecticut
New Hampshire
Nevada
Maryland
New York
Everywhere else, which is thirty of the fifty states, it is legal to fire someone simply for the suspicion that they are gay. It doesn't need to be proven as long as the suspicion is the basis for the firing (and not some category such as gender or race which does have protection). A parallel case would be one in which someone was fired for suspicion of having, say, Arab ancestry; even if they didn't, they'd be covered under laws against firing based on race or ethnicity.
There are some counties and municipalities in states not listed above which forbid firing on the basis of sexual orientation or sexuality as well, of course. Places like Austin, Texas; Alexandria, Virginia; Fort Lauderdale, Florida, etc. all probably have such laws.
