Work-around for Firefox is already running, but is not responding
I ran into the infamous message, "Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system."
I had no trouble starting a single instance of Firefox Portable, but once Firefox was running, if I did something like
Start/Run/k:\Portable\FirefoxPortable.exe http://www.google.com/ig
intending for it to open the link in the existing Firefox window, I got the message. I had set "AllowMultipleInstances=true" in FirefoxPortable.ini.
In *my* case, setting it to "AllowMultipleInstances=false" made the error go away. I was running FP2-RC3. I post this info in case someone else can use the info.