apologies if you already know about this one... it's always a risk when you put up a "tip" that you're the kid in class pointing out the "bleedingly obvious" and making everyone else roll their eyes...
anyway, I've been using firefox for a while now... I was a bit of an early adopter - but not one of the uber-early, but maybe in the third or fourth tier of early adopters... I have to admit that although I may have been using it for a while, I just replaced IE and took advantage of the tabbed browsing and a few of the extra features and extensions - mainly the developer extension and the search in the toolbar for searches on imdb and the dictionary etc.
One thing that I finally took 5 minutes to try and figure out is how to change the address bar searching from using google.co.uk to google.com.au. The Address Bar Searching that I'm referring to is when you type in something like "google shiny new gadget" into the address field (instead of www.google.com) and firefox automatically launches the google page with the relevant returns based on the search terms "shiny new gadget". Being in Australia the problem with this has been that it provides UK localised content instead of Australian - you end up with a bunch of hits from the shops on Tottenham Court Road in London - not quite what I'm looking for...