A short guide to installing flash player in Pale Moon browser in 2021.
1) Install Pale Moon browser from homepage, it can be 32-bit or 64-bit version (I am using 32-bit version)
2) Install older version of flash player from archive.org version Flash Player 18.104.22.1681 file flashplayer32_0r0_371_win.exe inside downloaded zip. You may choose "Never check for updates" while installing. You may need to uninstall your current version of flash before installing this one.
3) After installation create folder "plugins" in %PROGRAMFILES(X86)%\Pale Moon\browser folder and copy file C:\Win