Failure to install flash on Foxfire after 90%

Without knowing anything about your computer, it's hard to say.

If you haven't rebooted yet, that's a great place to start.  At minimum, it will eliminate a bunch of potential roadblocks for other steps.

If rebooting doesn't help, please see the installation troubleshooting guide:

Windows:

https://helpx.adobe.com/flash-player/kb/installation-problems-flash-player-windows.html

Links to the offline installers are at the bottom of the guide.

Mac:

https://helpx.adobe.com/flash-player/kb/installation-problems-flash-player-mac.html

Collecting and posting the logs would help us improve the product, and the links to the offline installers at the bottom of the guide should get you going.