Microsoft is testing the removal of Adobe Flash, that is scheduled for December 2020. By that time it will be discontinued in the majority of web browsers. KB4577586 allows you in advance to see right now what will happen.
Mozilla will completely remove Adobe Flash support from the Firefox browser in December, 2020. Version 84 of the browser won't include the code to load the Flash plugin.
Mozilla is going to discontinue support for Adobe Flash in Firefox 69. The plugin will be disabled by default. A new bug filing confirms this intention.
With the recently released Windows 10 build 15002, Microsoft Edge got a new security feature. Now the browser will block all untrusted Flash content on web pages you visit.