I want to run a windowed plugin under webrender，but the plugin does not display
1390440 Only support windowless plugin，windowed plugin only support OpenGL when disable webrender
Because there are still many application scenarios
This is not advisable. (Please wontfix.) From the perspective of Nightly, Flash support gets removed in 6 months in October (bug 1455897). With that, any support for windowed mode plugins will be removed, too. (bug 1296400 comment 10)
On Linux, WebRender is not enabled by default yet. Flash removal is also a blocker for enabling the Wayland backend by default. (bug 1543600)
In December 2020, Flash support will be completely removed from consumer versions of Firefox. Adobe will stop shipping security updates for Flash at the end of 2020.