Firefox 54 Is Rolling Out on Ubuntu, but Multiprocess is Disabled - OMG ! Ubuntu !
►http://www.omgubuntu.co.uk/2017/06/firefox-54-now-available-in-ubuntu

Mozilla describes Firefox 54 “the best Firefox ever”, and say its multi-process prowess, which splits tabs into separate processes, can help improve memory management, stability, and general web-browser peppiness.

And initial feedback from users seems to back those claims up.

But, crucially, multiprocess is disabled in Firefox for Ubuntu in the new update, meaning some of you reading this might not be benefiting.