I keep getting the message “Failed to read the configuration file. Please contact your system administrator”
I am the administrator. I’ve tried re-downloading, system restore, ccleaner, safe mode, etc.
I’m running a Dell, plenty of hard drive space, 4 gig of memory.
Firefox has worked fine for years until I downloaded Avast (Free) upgrade. Then everything went to Hell. I’m guessing I have a virus but don’t know how else to find it. Now using (Ugh) Explorer, which is intolorable!
Help?
https://support.mozilla.org/en-US/questions/909867
Have you tried this mate?
By “re-downloading” do you mean re-installing? According to this you want to remove the Mozilla Firefox program folder before re-installing. That folder doesn’t contain any of your personal information like bookmarks or cookies to it’s ok to remove.
If that doesn’t work, try this:
Diagnose Firefox issues using Troubleshoot Mode | Firefox Help
I remember some time in the past Firefox had a problem with an antivirus which declared one of it’s configuration files to be a virus, and then blocked all access to said file. If this is the case, you won’t be able to remove the Firefox folder while Avast is running, so try turning off protection temporarily if you have troubles deleting the Firefox folder.
You may also be able to set an exception for the specific file in question. See your antivirus’s documentation for how to do that. If Avast is causing the problem, that file would most likely be mozilla.cfg in Firefox’s main folder.
Note Firefox’s main folder is usually C:\Program Files\Mozilla Firefox or C:\Program Files (x86)\Mozilla Firefox.
Thank you all for your help. I finally had to re-install windows. 
Lost some things but cleared up a lot of others. It seems like every site wants to put in something extra like a toolbar or browser, etc.
It probably was Avast that screwed up my browser, I’ll never use it again!
Either Mcalfee or AVG, what do you think?
Gahd, yes, everyone wants their freakin’ spyware on your system in the name of “helping” you. So much of it is stealth-install, as well - miss that tiny checkbox in the install process for something you want (Flash and Acrobat come to mind - pit you, Adobe, for bundling that McAfee crap that way!) and you’ve got ineradicable garbage screwing up your system.
Any of the lightweight AV tools - as opposed to the “we’re going to bloat your OS to John Candy proportions to protect you against Martian diseases and chipmunk invasions” panoplies - are good. AVG AV, Kaspersky, even Avant if you restrict it. I have been very satisfied with AVG for years.
Thanks, AB, I think I’ll try AVG.
When Firefox goes bad on me, I back up the bookmarks to an HTML file in another folder, and delete everything labeled Firefox so when I reinstall it all the settings are remade. Otherwise it likes to keep the part of the setup that was causing the problems.