256MB of Ram isn't really "high" (depending on what you are doing). To put it into perspective. You aren't even using a 16th of your available RAM. AVG is a very poor system optimizer and anti-virus, and often provides false positives. You can try doing things like uninstalling add-ons you don't use: [[Disable or remove Add-ons]] Update your graphics Driver: [[Upgrade your graphics drivers to use hardware acceleration and WebGL]] Install all Windows Updates, and then test again. How many tabs and what were you doing when you received this alert? Did Firefox continue to run normally? You can view at any time how much memory Firefox is using by typing about:memory into the address bar.