Re: Installation won't complete, but Firefox can't be uninstalled, because installation isn't complete.
Here, I have a solution (from Windows 8). In the "Start" screen, right click on the Firefox app. Then click the "open file location" at the bottom of your screen. Highlight and delete all Mozilla files. THEN you can do a fresh download from firefox.com. (Here's what didn't help: starting in safe mode, uninstalling the software, running as Administrator.) Good luck!