not a dumb question at all, actually.
the truth is that anyone who presents outside of the gender binary has a more difficult time getting work, even counting people who just happen to dress more androgynously. However, Trans people definitely do have a more difficult time finding work, and if you come out in the US in a state where there is "At Will" employment, you may find yourself without work. It happens.
As for my own experience, I can definitely say that I have had difficulty finding work. I am currently in school, but even looking for summer jobs, or work when I was between my previous program and this one (currently doing post-grad work), has been difficult. I live in Canada, which is generally a much more accepting place, and there is still this difficulty, so I can only imagine the difficulty that someone would face in other, less accepting places.