Still not working for me, at least for Firefox.
Versions
Firefox: v55.0.3 32 & 64bit (fresh install), v53.0.2 32bit
Avast
Engine & Definitions: v170901-0
Program: v17.6.2310
Curiously, Waterfox & K-Meleon, which are forks from Firefox, runs smoothly. Vivaldi, which is Chromium based, also run without problem.
Whoops, is this the right thread to report browser (firefox) cannot be opened?