(Resolved) I can no longer open Firefox!

[Odin2]

The error message is:

XUL Runner
Platform ver. 63.0.3 is not compatible with
minVersion 64.0
maxVersion 64.0

What do I do to open Fx?

[DanRaisch]

Close all applications and reboot the computer.
Clear the browser cache (of whatever browser you are using to download FF) and the Windows Temp directory.
Download a new copy of the full installer from www.mozilla.org/en-US/firefox/all
Delete the directory C:\Program Files\Mozilla Firefox (or C:\Program Files\Mozilla Firefox (x86)
Run the installer.

[Odin2]

Many thanks, Dan! I'm back and running.

Is there something I might do to prevent a recurrence?

[DanRaisch]

Since we don't know what caused the problem in the first place it would be pretty hard to identify preventative steps.

[Odin2]

So the answer is No. (I thought you might in fact have an idea of what caused the problem.) I remain grateful that you got me back off the ground.

[DanRaisch]

You're welcome.