Forum Response - Platform version is not compatible message

If you see an error message that the Platform version is not compatible, this is a known issue caused by a corrupted installation after a failed update. The workaround is to uninstall and then re-install Firefox to fix this issue while our team is working on a more permanent fix. You shouldn't lose any data if you download the full installer from our official source.

See also Firefox won't start - find solutions (XULRunner - Error)