From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4a) Gecko/20030403
Description of problem:
There doesn't appear to be any way to unselect the product on any of the query
pages now. This is quite handy when you're searching for bugs, as you may want
to search in more than just the RHL product, if you know that there are other
products that have the same problem. Selecting all products is an option, but
the old default of not having a product selected was nicer.
Version-Release number of selected component (if applicable):
Can you use the control key when clicking the product? That should de-select the
product in the product list. This seems to work in Mozilla for me, and may be a
different key combo in different browsers.
Hmm, yes, that appears to work.