Recently I read an article on the Tor developer site about removing responses for certain calls to Tor programming built into Mozilla's code. By that token, and depending on what they remove, would it not be possible for a site to attempt to use commands removed in the package just to determine if the user were in fact using a Tor browser and not a more standard Mozilla distribution?
The data I refer to (found in my notes) appears to show concern for revealing information about the web browser being Firefox-based and what operating system is being used. The provided answer seems to describe reasoning why this is however not important:
A snippet from that site: In Firefox25, Mozilla added a couple scary media queries (-moz-os-version and -moz-osx-font-smoothing). I think we should get rid of these, as well as most/all of the prefixed media queries in https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Media_queries#-moz-os-version. Either just disable them, or make them lie.