All major browser makers plan to remove Flash support from their browsers in 2020. Adobe announced the deprecation of Adobe Flash in 2017 and companies like Google, Microsoft or Mozilla revealed plans to end support for the technology in their browsers. Adobe Flash won't receive security updates anymore from 2021 on.
Firefox uses a plugin system to integrate Adobe Flash, that is installed on the system, into the web browser. Google Chrome and other Chromium-based browsers ship with a native Flash integration instead.
The current state of Flash in Firefox is the following: Flash is disabled by default in Firefox but users may activate Flash on individual sites if they require it. Flash is the only NPAPI plugin that Firefox still supports; support for other NPAPI-based plugins such as Microsoft Silverlight was dropped in Firefox 52 which Mozilla released in 2017.