Firefox Nightly automatically sends feedback to Mozilla, (such as number of open tabs and windows; number of webpages visited; number and type of installed Firefox Add-ons; and session length) and Firefox features offered by Mozilla or by partners (such as interaction with Firefox search features and search partner referrals).
v58.0 [Oct 26, 2017]
Video decoding is disabled when not visible, providing both performance and limited battery usage.
I have been using Epic Privacy Browser for a few months now and I must say that I am really impressed