For historical reasons, many of the scanned pinball apron instruction cards that you can find for download on the Web are in SWF (Shockwave Flash) format. PinballY can display these instruction card files, but only if you install the Adobe Flash Player ActiveX control.
PinballY specifically requires the ActiveX version of the Flash Player. This is also known as the Flash plug-in for Internet Explorer. There are separate Flash plug-ins for other browsers as well, but PinballY can't use those. You'll need to install the ActiveX version even if you already have Flash working in Chrome or Firefox.
Getting the ActiveX version is a bit trickier than you'd think. Adobe's Flash download page tries to make things "easy" by automatically selecting a plug-in to match the browser you use to access the download page. But that actually makes things harder in this case, when you need a specific version. Here's how to override the automatic selection and get the version you actually need for PinballY:
The Flash plug-in comes in several versions for different browsers. Chrome uses one version, Firefox uses another version, and Internet Explorer uses yet another. Unfortunately, the different plug-ins have incompatible programming interfaces, so you have to separately install each one that you need. What's more, some browsers have Flash support built in, so they don't need plug-ins at all.
In the case of PinballY, the Flash ActiveX control (also known as the Internet Explorer plug-in) is the one that's needed. It doesn't matter if you have the Chrome version and/or Firefox version, since PinballY can't access those.
Follow the step-by-step procedure above under "What to install" to get the ActiveX version.
It's perfectly fine to keep all of the different plug-ins installed at the same time. Adding the ActiveX version won't affect any of the other versions you might already have installed.
Why in the world are we talking about SWF files when even Adobe considers them obsolete? Blame history. The first front end for virtual pin cabs was a program called HyperPin. It was the only option in the early days, so most pin cab builders used it, and when they shared media files online, they naturally used the file formats that HyperPin could work with. HyperPin happened to use .swf format for instruction card images. HyperPin isn't as widely used any more, but all of those media files that people uploaded (including all of those .swf instruction cards) are still out there. At some point maybe someone will tackle the big job of converting them all to modern image file formats and uploading new versions, but in the meantime, the path of least resistance is to install Flash Player so that you can use the existing .swf files without any extra conversion steps. (I've looked for options that would let PinballY perform the conversion automatically, but all of those also require installing Flash Player! And once you do that, you can view the .swf files directly, so it makes no sense to convert them at that point. If a free converter program or library comes along that works independently of Flash Player, I'll be happy to incorporate that so we can get rid of the Flash requirement.)
Just to be clear, PinballY doesn't require you to use SWF instruction cards! It's perfectly happy to display instruction cards that use ordinary image file formats like PNG or JPEG, if you can find them. The only reason we're talking about SWF is that many of the instruction card images available for download from the virtual pinball sites happen to be in SWF format, so we wanted to let you use those without doing any conversions.