Looking ahead to FF 57 (expected to be released Nov. 14) :
1) Firefox 57 will feature a new core engine, called Quantum, that purports to make FF 57 run twice as fast as FF 52 (released about a year ago).
2) FF 57's Photon User Interface will offer a new look for the entire browser.
3) Firefox 57 will replace the old Add-ons API with the new WebExtensions API. As a result, legacy add-ons that have not been ported to Firefox's new add-ons technology will stop working --- meaning that nearly 75% of all Firefox add-ons won't be available to users on the new version.
Windows 7 Pro SP1 (64-bit), avast! v17 Free, MBAM3 Pro, Windows Firewall, OpenDNS Family Shield, SpywareBlaster, MVPS HOSTS file, MBAE Premium, MCShield, WinPatrol PLUS, SAS (on-demand scanner), Zemana AntiLogger Free, IE11 & Firefox (both using WOT [IE set to WARN, FF set to BLOCK]), uBlock Origin, CryptoPrevent.
[I believe computer-users who sandbox (Sandboxie) are acting prudently.]