Well maybe not exactly zero, more devs using FF tools --> more websites designed to be optimized for FF first.
All the people I know, who left FF, myself partly included, did so for this reason. Quite some sites did not work anymore on firefox. And the normal user does not care that this is because of vendorprefixes which are not standard. They care about that their website does not work anymore.
Keep the webdevs ... keep your users.