When updating a previous version, I got the 'The update could not be installed' error. I uninstalled FF and then installed FF v35. Still have the issue. I looked and found problems with the parent.lock file - deleted any I could find. Same problem, error on restart I found a note about cleaning out the old updates after an install. I dug around and found one at: c:\Users\smann\AppData\Local\Mozilla\updates. I cleaned it out and, low and behold, no error! Then, I went into Help/About Firefox and checked for further updates. The problem has returned. What gives? How do I get FF to not complain. It appears to be working okay, but, it makes you wonder.