How to prevent flash from updating
Adobe used to have a fourth Flash tester but sometime in Jan 2014 or earlier, it was merged into the above.FLASH PLAYER on CHROME OS (created Oct 15, 2015) I ran into an interesting wrinkle while logged on as a Guest user on a Chromebook.The upside to being a guest user is that you always start with virgin copy of the operating system.
As of Chrome OS version 46 (and probably earlier versions too), Google defaults to "Detect and run important plugin content".
At one point, I was viewing a single web page and the Chromebook was sluggish.
I used Shift-Escape to bring up the Google Chrome Task Manager and saw that the Flash plugin was using a lot of ram and CPU cycles.
This site (page really) started as way for me to easily find the main Adobe Flash tester page (link above) which reports both on the installed copy of Flash in your browser and the latest version for assorted operating systems. Adobe has a second un-named tester page at adobe.com/swf/software/flash/about/flash About_info_that displays the installed version number in a huge font (also available with insecure HTTP). But, that's all it does, there is no indication of whether the installed version is current or not.
If your browser tries to download a file, Flash is not installed.