C:\Users\<user>\AppData\Local\Mozilla\Firefox\Mozilla Firefox\updates
(%LOCALAPPDATA%\Mozilla\Firefox\Mozilla Firefox)

If files already have been downloaded then you need to remove the files in the updates and updates\0 folder. You can delete active-update.xml and updates.xml as well if present. C:\Program Files\Mozilla Firefox\updates Vista: C:\Users\<user>\AppData\Local\Mozilla\Firefox\Mozilla Firefox\updates (%LOCALAPPDATA%\Mozilla\Firefox\Mozilla Firefox) The "Application Data" folder in XP/Win2K and the "AppData" folder in Vista/Windows 7 are hidden folders. *http://kb.mozillazine.org/Show_hidden_files_and_folders ---- If there are problems with updating then best is to download the full version and uninstall the currently installed version. Download a fresh Firefox copy and save the file to the desktop. * Firefox 5.0.x: http://www.mozilla.com/en-US/firefox/all.html * Uninstall your current Firefox version. * Do not remove personal data when you uninstall the current version. Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer. * It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling. Your bookmarks and other profile data are stored elsewhere in the Firefox Profile Folder and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox. ---- * http://kb.mozillazine.org/Profile_folder_-_Firefox * http://kb.mozillazine.org/Profile_backup

The program must close to allow a previous installation attempt to complete * https://support.mozilla.com/en-US/kb/The%20program%20must%20close%20to%20allow%20a%20previous%20installation%20attempt%20to%20complete Check and tell if its working.