Adobe Flash is a multimedia platform commonly used on the web to provide interactive and streaming content, including DRM content such as music or movies. It is becoming less utilized in favor of HTML5, but a lot of content is still only available by using a Flash plugin. Adobe is planning to end-of-life Flash  in 2020. Many browsers have already removed the flash plugin from default installs and require special steps and plugins to install, but not all browsers support flash.
Flash in Firefox/Other Browsers
Adobe's official Flash plugin can be installed for use in NPAPI-compatible browsers like Firefox. adobe-flash-plugin must be built with Xbps-src. Additionally, you must allow restricted packages to be built.
$ cd void-packages $ echo XBPS_ALLOW_RESTRICTED=yes >> etc/conf $ ./xbps-src pkg adobe-flash-plugin $ sudo xbps-install --repository=hostdir/binpkgs/nonfree adobe-flash-plugin
- Adobe Corporate Communications "Flash & The Future of Interactive Content" Adobe Blog