As of VPS v170901-0 Firefox still not working for me.
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.