Why Firefox 21 Crashes

Every new version of Firefox comes with new features. Recently, users of Firefox 21 reported that their browser crashed after clicking the close (X) button.

What is the cause?

Firefox was experiencing trouble with hardware acceleration. To fix this, disable it by going to Tools > Options > Advanced > Browsing and unchecking Use hardware acceleration when available. This is a known issue in certain Firefox builds.

If you are still experiencing issues, I recommend visiting the official Mozilla Support page for help.