I clicked my heels together 3 times and asked Firefox not to change anything else, but I don't know if it worked... In the meantime, which FF version did you upgrade to, and what happens (if anything) when you click the HL button?

For me, HL works, but sometimes produces the little text window very slowly. It seems more dependent on the target page loading entirely, whereas before it didnt' seem to matter much. This began happening to me two FF updates ago.