Long time firefox user here, so when they asked me to replace firefox with chrome when i instaled avast 7 i refused. Since then, every time i reboot my computer, avast try to install chrome. Will its stop at 1 point or i have to change antivirus?
are u running win 7 or win xp…
uninstall avast 7 by using tool provided here: www.avast.com/unintall-utility
now download and re-install avast and that should fix it… 
There is much discussion in the forum under Free/Pro Version about this issue. You can see one here: https://forum.avast.com/index.php?topic=100380.45 - see my last post on page 4 - You need to do a Custom install and untick install Chrome, which is default for Avast install, but see my post for more details.