Another thing worth noting is that if you are using Debian-rebranded Firefox (Iceweasel), you have a very unique user agent that is easy to track.
There is a bug opened (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=748897), but as far as I know, no simple solution exists yet. You can change the user agent with an extension to keep it identical with the most popular Firefox version, but then you have to manually keep it up-to-date.
EDIT: seems that this extension need to be updated, sorry...
But I don't know, if you allow javascript maybe you will leak your real user agent?
I like to switch between iceweasel and seamonkey, and I'm "proud" of my different and unique user agent :)
Speaking of privacy, actually I'm more concerned about referer, third-party sites, content delivery networks and so on.
There is a bug opened (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=748897), but as far as I know, no simple solution exists yet. You can change the user agent with an extension to keep it identical with the most popular Firefox version, but then you have to manually keep it up-to-date.