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.
Adobe Flash can be used to play videos and animated content. These days, there are a large number of users who disable Adobe Flash. They do so because of performance and battery life reasons as well as because security vulnerabilities are discovered in the Flash plugin. Security vulnerabilities can be exploited to hack your PC. Most of the media web services and sites have already switched to HTML5 videos, so Flash is no longer require to explore their content.
Adobe Flash is now the only NPAPI plugin that Firefox supports. Starting in version 84, Mozilla will remove all NPAPI code from the browser which is required to run Flash. Chromium-based browsers will also drop Flash support starting with Chromium version 88 which is coming on January 2021. And at about the same time, Adobe will also end support for Flash.