How do I get the flash player pop up

The bottom line is that browsers have introduced restrictions on both how *all* content can access the Camera and Mic, and how Flash Player is executed.  Omegle and Chatroulette need to update their sites, but I get the impression that they either don't have the resources, or they've moved on to other priorities.  Ideally, they'd just reimplement the services with WebRTC -- you don't need Flash for web-based cam chat in 2018.

That said:

Most browsers now require that all content on the page be served over HTTPS in order to gain access to the Microphone and Camera.  If the page isn't loaded over HTTPS and/or the lock icon is not displayed, the browser is unlikely to allow anything to access the Camera and Mic, including Flash.  If the page is loading over HTTPS, but they're including ads over HTTP, that's a problem, the lock icon should not display, and the mic and camera will not be accessible until they fix it.

In Chrome, you can click on the lock icon next to the address bar to adjust permissions for a given site.  You can explicitly allow Camera, Microphone and Flash.  At that point, Flash can see that the computer has a camera and mic available (until you allow the camera and mic in Chrome, it will just return an empty list of devices to Flash), at which point, we can then throw our own camera/mic prompts.

If this sounds convoluted and likely to break content that isn't explicitly designed for that complex set of behaviors and states, you would be correct.

You can also explicitly allow access to the camera and microphone from Flash by right-clicking on Flash content and choosing Settings, then checking the Privacy tab, (and the Camera/Mic tabs to ensure that Flash sees the right camera and microphone, and that they're selected and working).

You might have to manually enable every possible Mic/Camera permission in both the browser and Flash, then refresh the page before it will actually present you with a usable application.