Ok. AVG normally don't prevent websites from being viewed.
What sites exactly did it block? Are you connected by a router or directly to the internet?
Solution
Note that in this case, uninstallation and re-installation of Firefox will not solve the above difficulty.
Making a reset of Firefox will set off the trouble. Below is a means of how to proceed:
1. Click on Start / Run Enter the following command: firefox -safe-mode
2. In the open window, select "Reset preferences to default Firefox"
3. Click on 'Make the changes and restart "
You can now browse properly on Firefox.