Firefox Crashing when ask AVG to update manually

Mary,
Thank you for reaching out to us with your concerns. We appreciate all your efforts in trying to fix the issue, we apologize for the difficulties. Microsoft have stopped the updates to all the browsers and this may be the reason to this issue. We request you to reinstall your Firefox browser and then repair avgclick.me/RepairAVG your AVG program to check with this.  
Please feel free to get back to us for any issues with AVG. Thank you!

I am suffering a lot of crashes with Firefox at the moment. I have tracked it down to the possibility that AVG Free is causing this problem. I have noticed this has happened since AVG Zen is added to AVG and if I ask AVG to check for updates it suddenly slows the computer and then the screen goes blank and turns off the computer completely. I make sure my computer is always clean using check disk etc., and even done a thorough checkdisk/repair from the main dos prompt to ensure no bad sectors causing my computer to crash (taught me by a qualified computer expert to ensure my computer is clean and firing on all possible cylinders).
Suddenly my computer turns itself off for no reason. I have followed several options such as "Refresh Firefox" from the Troubleshoot menu as shown on Youtube and this suggested this would reinstall bookmarks. This method did not do so but as I know how to Restore bookmarks I did this myself. I have not, however, used the method on the internet of creating a new profile. I decided that as I have now become aware that AVG seems to be causing this problem and therefore it may well be that whilst on the internet if AVG decides to update itself at some random time this could therefore be causing my crashes as I discovered this morning when I asked it to do so it crashed. I feel therefore that AVG may well be the problem.
Can you suggest?
I don't want to buy a new computer - I have Windows XP Service Pack 3 and know my computer is working as well as it could as I am fairly computer literate. I have recently been sent a Wireless modem by Telstra which I have had to load for the forthcoming NBN and even wondered if this could be causing it. But I do feel I have narrowed it down to AVG Updates?
Or maybe Christmas overload?? I really wonder if anybody can give me a suggestion.
Kind regards
Mary

Mary,
Thank you for reaching out to us with your concerns. We appreciate all your efforts in trying to fix the issue, we apologize for the difficulties. Microsoft have stopped the updates to all the browsers and this may be the reason to this issue. We request you to reinstall your Firefox browser and then repair avgclick.me/RepairAVG your AVG program to check with this.  
Please feel free to get back to us for any issues with AVG. Thank you!