I could not restart firefox after I closed the window of brower's.
Sometimes I could not restart the firefox after I close it, the warning reads "The firefox is already running, but it is not responding. To open a new window, you must first close the existing Firefox process, or restart your system."
It's quite bothering that I have to terminate the process to start it again.
Opaite Mbohovái (2)
See "Firefox is already running but is not responding" error - How to fix, in your case it appears to be caused by Firefox hanging when it closes, for more details on that see hang at exit.
Your plugins list shows outdated plugin(s) with known security and stability risks.
- Java Plug-in 1.6.0_13 for Netscape Navigator (DLL Helper)
Update the Java plugin to the latest version.
- http://java.sun.com/javase/downloads/index.jsp#jdk (you need JRE)