I forgot to say the OS is Vista and the browser is Chrome

What happens when you run the installer?

Let’s do a full clean re-install; Download Firefox For All languages And Systems {web link} Save the file. Then;

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Mac: Open the "Applications" folder. Linux: Check your user manual.

Do Not remove the profiles folder.

Look for, and rename any Mozilla or Firefox program folders by adding .old to them. Do not rename the Mozilla Thunderbird folder.

After rebooting the computer, run a registry scanner. Then run the installer. If all goes well, remove the OLD folders when you are done.

If there is a problem, start your Computer in safe mode and try again.

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Sorry but none of your options work. The message that I get tells me that a previous uninstall was not completed and I must restart the computer to complete it. This tells me that the problem is probably in the register.

An additional piece of info is that all files in the Mozilla folder are marked "read only" Would that not make it appear that Firefox is running when, in fact, it is not?

Those files should not be read-only. Did you do the re-install as I instructed above?

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Try to run the Firefox program once as Administrator (right-click: Run as Administrator).

Note that Windows shows a green block in the Read-only box for folders, but not a check-mark. Only a check mark in the Read-only box means that a folder or file is Read-only. Windows doesn't check all the files in a folder, so instead displays a green block to indicate that it is not sure. You can look at each file individually to see if any are read-only. Easiest to do that is to make the Attributes visible in "View > Details" mode: Choose Details in Windows File Explorer.

Thanks for all of the suggestions but I found the problem. FYI recall that I said the error message was not allowing a new install because Firefox was running in the background due to an uncompleted uninstall run sometime in the past. It suggested that, if I restarted the computer, it would repair the problem; it did not, and that's when I turned to this board for help.

I have since discovered the executable in the Firefox folder but it had an extension (such as .old) attached to the name. I removed the extension, clicked on the file and behold Firefox opened. I was then able to install the new version without a problem.

That was very good work. Well Done. Please flag your last post as Solved Problem so others will know.