It appears as though the engineers have added that one new feature that makes Firefox unsalvageable.

Not only did the update to Version 50 fail but I then removed Firefox and tried to re-install it ... twice. Both times the end of the download/install process was a jump to a blank screen with a blank taskbar at the top and then ... nothing.

Did you try to remove the install folder of Firefox in %ProgramFiles% and all Firefox entries in the Windows registry? After that, you should be able to reinstall Firefox.

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

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

Windows: C:\Program Files C:\Program Files (x86) Mac: Open the "Applications" folder.
https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory.

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 if there is one.

After rebooting the computer, run a registry scanner if you have one. 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

I am still unable to re-install.

When I click on the installation file ("Firefox Setup Stub 50.00) on my desktop I'm told "Windows can not access the specified device, path or file. You may not have the appropriate permissions to access the item." and the only option is to stop the process.

Use the link I posted above to get the Full installer.

When I click on your link, I'm taken to a download site for Firefox in about 50 languages. The US English icon only downloads the Setup Stub, not the full file. There is no "Full Installer" unless you are referring to something else. The only thing that looks like a "full installer" is under the heading of "Mac".

That is odd, I called for more help.

Any news?

Windows cannot access the specified device , path, or file ... https://support.microsoft.com/en-us/kb/2669244

Well. Like all good military commanders I have a Plan B ready. If fact, this was Plan F. I went straight to it. After turning off Trend Micro, I started the installation and it zipped right through it.

Only thing, I can't recall how to turn on the toolbar that has the "About" choice so that I can see my version number.

At any rate. Thanks to all an this very wonderful Thanksgiving Day ... and especially to FredMcD.

Eric

That was very good work. Well done.

Press the Alt or F10 key to bring up the toolbar. Then Help > About Firefox will tell you what version have and check for updates.

or

Type about:support in the address bar and press enter.