|i have not heard of poison ivy, but i see this happen with my FireFox every now and again. It sounds less like a virus and more like the app is crashing but not completely.|
What version of Firefox are you using? The newest is 3.0.6, and you should be on at LEAST 3.0.5 because it addressed several security vulnerabilities.
If your version is already updated, try repairing the installation or reinstalling, and see if the problem persists.