I have questions about issues I'm having with Firefox. Which web site in the Stack Exchange network is most appropriate for software related questions?
Clarification: yes, this is a usage question, not programming related.
SuperUser, I believe.
From the FAQ:
If it's about Firefox programming (like XUL or Greasemonkey plugins), try Stack Overflow.
If it's about Firefox usage in a "super user" manner that could be useful to other super users, go to Super User.
As Jeff says: