Ubuntu fails to start the following applications:
When i try opening Mozilla Firefox or Thunderbird it says "Firefox is alresdy running, but not responding . To open a new window you must first close the exsiting firefox process, restart your system. Also neither of the LIBRE applications run.
My first question would be, have you restarted your computer? This can often correct many issues. Which version of Ubuntu are you running?
Next, try running the System Monitor application (gnome-system-monitor for Unity or GNOME desktops) and look for those processes running in the background. Sometimes these programs stay running in the background even after you click the X. You can use System Monitor to forcibly end those processes and then you should be able to launch the programs again.
