User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9b5) Gecko/2008032620 Firefox/3.0b5 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9b5) Gecko/2008032620 Firefox/3.0b5 I exited Firefox, it asked me if I want to save my tabs. I said no, I do not want to save my tabs. Then I quickly reopened it. When I reopened the program, it said "Firefox is already open but not responding." I think that Firefox was not completely closed and this is the reason the error popped up. (Although it was completely gone from the task bar) Reproducible: Couldn't Reproduce Steps to Reproduce: 1. Several Tabs 2. Close Firefox 3. Open Again Fast? Actual Results: Program opened fine when I tried to reproduce it.