Hi Paul, when you uninstalled Firefox, did you specify that you wanted to remove your personal information as well as the program files? By default, the information is preserved, since it includes bookmarks, saved passwords, add-on data, and other content the user may need to migrate to another browser or another system. As you noted, this is stored under %APPDATA% (profiles) and %LOCALAPPDATA% (cache/temp).

I don't know whether there is a good and up-to-date document on what Firefox's installer adds to the Windows registry. Does your toolkit include any monitoring programs that allow you to log what the installer does? I used to use InCtrl5 in the Windows 9x days, but its successor, InCtrl X is no longer free (http://www.pcmag.com/article2/0,2817,2398835,00.asp). If all else fails, a before-and-after registry export and a text comparison program like WinMerge might fit the bill.

I should note that other programs often create or modify keys containing the word Mozilla when they advertise a Netscape-style plugin or a Firefox extension. You wouldn't want to clean those because they belong to other programs.

The removal of Firefox should not cause problems like that. Did you have problems before?

Perform a System File Check to fix the corrupted system files http://www.sevenforums.com/tutorials/1538-sfc-scannow-command-system-file-checker.html

Troubleshoot Firefox issues caused by malware {web link}

Uninstall Firefox from your computer {web link}

Oh wait, you can't install Firefox so you can't conduct that test. What is the error message you are getting when trying to install? Also, are you using the "full" or the "stub" installer? Full installers are available from this page (scroll down to your preferred language): https://www.mozilla.org/firefox/all/

Hello,

 The computer is from a client 3 hours away.   Mozilla Firefox was having issues and I couldn't resolve them and so I decided to un-install Mozilla Firefox using standard protocol to then attempt to re-install.  I also uninstalled the personal data via the instructions from the Mozilla Firefox support website.  Since it is not my computer there is no installation monitoring program running and did not believe I needed monitoring since it appeared to be a simple tune up of the computer.  
 At this point it appears part of Mozilla Firefox did not uninstall completely and causes Ccleaner when cleaning to fail.  The incomplete installation also prevents the re-installation of Mozilla Firefox, which sometimes is the fix to either repair or the re-installation can then allow a corrected un-install.
 In RegEdit.EXE there are several locations where there is Mozilla, Firefox and I noticed Netscape.  I'm sure that by simply deleting the correct Registry line that it will allow Ccleaner to function and the re-installation of Mozilla Firefox.  I simply don't know which lines in RegEdit I can safely delete to remove enough of Mozilla Firefox safely from Windows 7 64 bit without causing damage.
 If you happen to know a safe way to delete specific key lines in the registry then that would be helpful

Thank you for your input. Paul

Hello,

 Yes.  The reason I tried to un-install Mozilla Firefox is that it was having functioning problems.  The goal was to un-install and remove all personal data, do a basic Ccleaner registery clean, re-start the computer then reinstall Mozilla Firefox.
 After the restart, Mozilla Firefox would not re-install and Ccleaner failed to clean temp files at about 40% marker when it said it was trying to clean Firefox, but Firefox had been uninstalled.
 There was no installation monitoring software since it is a clients computer 3 hours away.  I had no reason to have install monitoring program installed since it was a basic tune up.

I will use your advise to do a System File Check to see if I can find any errors. I believe that if I can find specific and safe registry lines to delete then it will also fix the problem. In the registry there are several locations where Mozilla and Firefox locations listed but I don't know which registry lines I can delete to solve the problem.

 Thank you for your input I will try a System File Check scan to see if I can find a problem.

Paul

Hello,

 After doing a System File Check, I will try the full install link you provided.  I've been using the standard Web Page install location.  It is possible that if I can get Firefox to install properly, then Ccleaner will also work when it tries to clean the temp files.

Thank you. Paul PS You guys are awesome in your quick response and advice. Many thanks to you all.

Firefox should not interfere with anything. Have you tried another scan / repair program? I think there are some free ones out there.

What kind of issues does that client's computer have?

Some issues can be caused by with hardware acceleration or malware and a (re)install won't help in such a case.

• https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration
• https://support.mozilla.org/kb/troubleshoot-firefox-issues-caused-malware