For a long time I did the same because some websites would refuse to load when they thought you weren't running Chrome even though it would have worked just fine in FF.

Are you suggesting that ff traffic would be substantially higher if I were to account for users that were obfuscating their user agent header?

And blocking your tracking data (that FF does out of the box)?

Well, maybe. I don't know the usage patterns of your site. And from that interaction, I'm not sure you know either.