I’ve tried also FF 41 beta but still no problems…
You can try to turn off stream filter which is new component in XP build. If you add following lines to C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast\WebShield.ini and REBOOT then original redirecting filter should be used:
[General]
UseStreamFilter=0
For those trying this you need to use notepad, to edit the webshield.ini as that is the only text editor that the avast self-defence module will allow. You will get a self-defence module question when you try to safe the changes, answer yes.
NOTE:
Another point, if the user hasn’t made any changes then the WebShield.ini may not be present. If so you may need to make a couple of changes in the Web Shield settings, shut down the web shield (that effects the changes made) and restart the Web Shield. Now you should be able to find the webshield.ini and effect the changes mentioned, for those changes to be applied the web shield may need to be closed and opened for it to use the new webshield.ini settings.