I don't think this is necessary anymore with total cookie protection being enabled by default https://blog.mozilla.org/en/products/firefox/firefox-rolls-out-total-cookie-protection-by-default-to-all-users-worldwide/
Not sure if it was just released today, but I got the email update about it just now. I'm pretty excited about this because I mostly just want VPN for web browsing, and the linux app kinda sucks.