Unfortunately, through trying to uninstall firefox completely with revo uninstaller I ended up with the trovi browser hijacker.............
I have been able to sort this out with a system restore, thankfully, and scanned and removed all the offending entries with Malwarebytes and all is now clear.
I have since reinstalled and uninstalled firefox and again reinstalled............(not using revo)
I have also uninstalled avast and reinstalled.............
I am still having the exact same problem
The icon for the avast extension in firefox is greyed out............when I click on it, yes there is an option for settings..........but this is still what I get when I do this, in the address bar
chrome://wrc/content/options.html
and a blank page!
I do not have Google Chrome installed, but the settings tab is sending me here for some reason

When I installed Avast I unticked the options for google chrome and for it to be my default browser..........
I have tried everything my end now..............
Thanks for all your help so far, and I really hope to get to the bottom of this somehow
Could it be a glitch within the latest Avast program?