This kind of works. Set a UA for all sites.

https://addons.mozilla.org/en-US/firefox/addon/uacontrol/

https://addons.mozilla.org/en-us/firefox/addon/user-agent-js...

String...

Mozilla/5.0 (Windows NT 6.1; WOW64; rv:42.0) Gecko/20100101 Firefox/42.0

Update the string every now and then?

https://techblog.willshouse.com/2012/01/03/most-common-user-...

Disable all plugins.

Best I got, sorry.

You can just use about:config if you're going to update it manually. But that's not nearly the worst part of fingerprinting, with plugins and fonts and apparently webgl, etc.

Is there a way to pretend plugins are disabled when they're on click to play?

I don't think so.

Also, being able to toggle the UA and setup lists to dynamically set it is helpful in my usecase.

Yes, everyone knows you can change the user agent string, but how do you change the list of plugins returned by the browser? Do you have to actually patch the binary?!

You can set plugins.enumerable_names to the empty string, or to the plugins you want returned. Unfortunately, this was recently removed.[1]

[1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1169945

navigator.__defineGetter__('plugins', function(){ return new Object(); });

Of course, you'd actually have to do a bit more work to make it bulletproof (otherwise fingerprinters could use the fact that you modified your default navigator object as a way to uniquely identify you !)

I imagine ultimately it's almost impossible to defeat fingerprinters in JS, as they could do tricky stuff like timing attacks to get you.

Use NoScript if you're concerned.

What plugins do you have installed? Given Chrome doesn't support NPAPI plugins anymore I'd think nearly all Chrome users would have the exact same plugin list. Firefox is also planning to remove NPAPI plugin support so I except the situation to be similar there in the near-ish future