Bear in mind you can launch separate Firefox profiles that keep distinct caches/cookies/passwords etc
There will undoubtedly be browser fingerprints by using profiles on the same machine (IP, super cookies, canvas etc), but there's going to be fingerprints using the same VM setup too and using a plugin like this wouldn't change that fact. Making each firefox instance truly unique would be a fair bit of work.
Multiple profiles can be pretty easy to maintain. Irony of ironies I created a setup using multi profiles to scrape 10 million FB profiles (just public data, though, and using about 4000 profiles on the same machine) and the cherry on the top was that FB anti-scraping mitigation is one of the most stringent of the social networks. Outside of tracking it did seem to be more data input orientated than client fingerprints (other than IP)
The anti-FB data-collection angle is a nice PR coup, and FB is probably being less than aggressive ATM given the bad press.
Surely it's a case of 'best efforts' to keep thing separate, given all the tracking methods going about (see that recent one using CSS).