You don't need to do anything to use this on swfchan, just have a ticked checkbox above.
Functionality is limited but can work decent on older flash files. If Ruffle seems outdated go tell me to update it in this thread.
Notably ActionScript 3 doesn't work with Ruffle yet, neither does blur nor glow filter effects.
ProjectorAdobe's offline Flash Player is still available for download on their site and it is what I recommend if you want a simple yet reliable way to watch flash files.
Save flashplayer_32_sa.exe somewhere on your computer (no installation needed) and here on swfchan you uncheck the "Embed" option. When asked what to do with the swf file you tell your browser to "Open with" the projector exe.
The flash will be downloaded to a temp location and then automatically viewed in flashplayer_32_sa.exe.
PluginEither install an old version of the official plugin or the last version (which is bricked by Adobe) and then replace it with a fixed version. Check here for resources and instructions.
There's an official way of getting the last plugin to work by editing mms.cfg but it is flawed with -in-filename issues, better to just swap out their bricked plugin. Search this thread if you want info about mms.cfg.
With the NPAPI plugin you can view flash in your browser as long as it still supports NPAPI. With the ActiveX plugin you can view flash with a seekbar in MPC-HC.