Hi leGarde, and welcome to Sparky.
Uhoh, Flash... well that is a red and irritated sore point. I am not sure if I can help you any more than paxmark1 already have done. I will give you the link to the Debian wiki of course, but doubt that you will feel helped by that. But I `ll do it anyway https://wiki.debian.org/FlashPlayer
My suggestion is that you sit down and take a really hardcore Google session about Flash Player, Linux, Debian etc... to collect information about it, to sort of understand how it works in Linux in general, and Debian in particular. I have Googled a bit, but mostly it is about how to install it on different distros. Not much about how it works, and why it works, or rather not works. I am pretty sure that the information is out there, just me that did not search long and hard enough.