Same here. You can have the buttons link to the firefox program itself, but that is about it... Sorry.
And I have sent a couple of nasty e-mails to Logitech about the issue -- and they (and me) have been ignored.
Simply stated, if hardware review sites (such as Anandtech) would ding Logitech for this kind of behavior, they would be more likely to fix it. An article is harder to ignore than an unhappy user or two...