There have been multiple separate initiatives over the years to speed up various aspects of Firefox. The largest one is culminating in the release of Firefox Q

There have been multiple separate initiatives over the years to speed up various aspects of Firefox. The largest one is culminating in the release of Firefox Quantum, which is launching as Firefox 57 tomorrow. You've heard this more lately as the Quantum version of Firefox was released to Nightly and then Beta/Developer channels over the past couple months.