Avast: 2014.9.0.2011
Firefox: 26
Operating system is windows 7 64 bit.
Thanks for that.
I am using 2014.9.0.2011 Free version
Firefox 25.0.1 (I don't like what has happened to the download manager in 26)
Operating system windows 7 64 bit.
More specifically, whilst AOS did work with Firefox, and IE, I don't Avast AOS installed for either. I have all three shields installed.
I don't have intelligent stream scanning enabled in the Web shield, but I do have scan for unwanted PUPS enabled.
My router is a wireless router, but connected to my desktop via ethernet.
So with a system notionally quite similar to yours, I have no problems accessing my router settings via Firefox.
Question, are you by any chance using a Zone Alarm firewall?.
I have a friend experiencing a similar problem with some web pages not fully showing and others that don't access at all. They all work OK if he uses another AV with his ZA firewall, or with Avast if he removes the Zone Alarm firewall. The latest fixes to the web shield didn't resolve the issue, nor did uninstalls, cleanouts, reinstalls.
He has reverted back to Avast 2014.9.0.2008 and that is working OK with Zone Alarm.