I have noticed on some website that firebug is off while on other sites it is on. I have not made any changes to these settings but how does a site tell firebug to turn off or how does firebug know do not turn on for this site?
Firebug remembers which sites you used it for. Here's an example. Go to a website and turn Firebug on. Now close out. Then, go to my site, www.mitchseymour.com (I'm using my site because I highly doubt you have ever been there before). Firebug should not be active. Now, revisit the site you just used FB on, and it should show up again.
Hope this helps.