System is W10 X64 Ent. 1703 build 15063.674 I was running V 56 x64 of Firefox no issues. Read that V 57 is out so went to about and tried update, then the problem started Failed to read the configuration file. Please contact your system administrator. Followed all instructions on uninstalling and deleting Mozilla folder from program files and eventually from %APPDATA%\Mozilla\Firefox\Profiles. rebooting. Reinstalling the full install download. No good. Same error. Tried with -P switch and created a new profile and the same error. So ended up uninstalling, delete folders, clean reg. and downloaded full install of V56 and it is working now. V57 needs more work, I think.