If you previously used the browser and closed it, but you decided to open it again to check something else and it didn't start, it is very likely that the browser failed to close properly.
To resolve this issue you need to close the browser via the Activity monitor. Open the Activity monitor, then find and select the web browser and click the "X" button in the top-left corner.
Check out the don't know how to quit programs / applications tips to learn how to deal with unresponsive programs.
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.