In addition discuss about if your Browser (Mozilla Firefox) is already but not running. To troubleshoot these problems you must close all programs to allow a previous installation attempt to complete, Restart browser. I hope that is provides Browser Support to solve this problems
Follow the steps to given below:
In Windows Vista If you are receiving the above error message while attempting to start Firefox, try to restart the program. If the problem persists, do the following:
1. Restart your computer.
2. Select the Start Menu in the Windows Taskbar.
3. In the Search box, enter the following:
%APPDATA%
4. Press Enter.
5. From the Application Data folder, navigate to Local\VirtualStore\Program Files\Mozilla Firefox.
6. Delete the file xpicleanup.dat.
7. Restart Firefox.
In Windows XP
1. Click on the Start button and select Search to open the Search Results window.
2. On the left side of the Search Results window, click on the All files and folders link.
3. Click to expand the More advanced options list.
4. Put a check mark next to Search system folders, Search hidden files and folders, and Search subfolders.
5. In the All or part of the file name field, type xpicleanup.dat.
6. Click Search to begin the search.
7. If any results are returned, delete them.
8. Restart Firefox.
