You have something that works out of the box, and something that doesn't.
Doesn't matter why it's your fault, you are using it wrong, it's your operating system, you aren't holding it properly these are the excuses of poorly designed products.
Web developers continue to use an inferior solution to deliver rich content on the web.
Adobe offers such technology under a nonfree license.
Open source browser Firefox can't include flash because of the license.
Purely open source distros also cant include this.
Oems can and should ensure end users don't have to worry about this.
Distros less concerned about purity may choose to set this up for their users.
Not only is this not mozillas problem it's a wholly imaginary one. The set of people who CAN install their OS but are incapable of installing an additional package is very nearly the empty set or at least it will be when said user doesn't learn to install software on their shiny new OS.
If that's too hard tell the people that work on the package manager gui and tell them how they ought to do better. The answer however isn't making it easier to go to the vendors website and download an exe.
The ficticious grandma that people want to cater to will experience Linux when it comes preinstalled on the pc she bought at Walmart and if flash doesn't work out of the box tell dell.
You have something that works out of the box, and something that doesn't.
Doesn't matter why it's your fault, you are using it wrong, it's your operating system, you aren't holding it properly these are the excuses of poorly designed products.