Separate names with a comma.
I am not quite sure this is the proper solution, but i had the same problem until i changed language & format settings and restartet the system....
The "top bar" uses the default style from elementary. I don't know an easy way to change it, as i affects much more than just Firefox. But you...
Just right click in the url bar/search bar and select "manage search engines". This is a long known "problem" but it seems like the developers...