How to un-block Flash "Blocked plug-in" for older Flash in Safari 5.1.10?

No, nothing in that support article is relevant. First of all, it is about current versions of Safari and Flash, so that none of the options/setting described even exist in the version of Safari that I have. Second, the topic of the support article is about how users can adjust the various normal settings which are under their control.

But my problem is different: Everything involving Flash is fine and correctly installed and "on" according to my computer: What has happened (as of a few years ago) is that Apple has somehow caused all out-of-date versions of Flash to display a "Blocked Plug-in" message to prevent security breaches, and to not function. There were all sorts of news articles about this (see Apple Blocks Out-of-Date Flash Player Plug-ins in Safari [Updated] | The Mac Security Blog) for example). But I don't know the mechanism by which Apple has implemented this. What I'm trying to do (and what millions of people with older Mac OSes are trying to do) is figure out how to disable/reverse/override the "block Flash plug-in" mechanism so that we can get Flash working again.

As I said in the original question, I cannot update Flash any further, because I am using an older OS (10.6.8) and this is the last version of Flash that works with this OS version.

The question is not how to update Flash, but rather how to "un-block" the plug-in for the version I currently have.

And I don't want to uninstall Flash, because I'm trying to get it to work, not trying to get it to go away.

As far as third-party browsers are concerned:

Only Google Chrome still successfully loads the Flash plug-in (and that is how I currently access sites that use it). All the other browsers I have tried, such as Sunrise, Firefox, etc., also display a "Blocked plug-in" error message for sites that have Flash.

The problem for me is that Google Chrome is not my default browser, and is a huge memory hog, and whenever I launch it to use it, it slows down my computer tremendously -- so I don't like using it.

I'll check to see if various Web sites have an "iPad version," but that would be a laborious case-by-case investigation as they crop up. In my experience, there still seems to be plenty of Web sites that unfortunately use Flash -- I haven't noticed that its use is dwindling. And because of that, I still want Flash to work for me. On Safari -- my out-of-date Safari.

The workaround you suggest seems vastly more complicated and expensive than just finding a direct answer to my specific question. Instead of buying one brand-new computer, buying and then installing OS X 10.6.8 Server in a virtualized environment, then transferring hundreds of GBs of data to the new computer, then possibly buying two additional old computers "as spares," then also having to learn (and teach others who share this computer) all the ins-and-outs of the new Mac OSes ("Sierra" or "High Sierra" or whatever the latest is), all for the sole purpose of getting access to the Flash plug-in, seems like extreme overkill. I just want to do one simple thing -- unblock one plugin (Flash) for one application (Safari). I know it must be possible, if I only knew how, and I'm pretty sure the solution, once found, will likely be fairly quick and easy. The hard part is finding out what needs to be done. The doing-of-it, I bet, will probably take five minutes.

For example, this article, https://eclecticlight.co/2016/01/25/inside-the-os-x-blacklist-xprotect/, explains that for a slightly later version of Mac OS ("El Capitan"), to unblock any plugin it is a simple matter to navigate to /System/Library/CoreServices/XProtect.bundle and go to XProtect.meta.plist, and XProtect.plist where the "blacklist" of blocked plugins resides, and one can then manually edit the blacklist by removing Adobe Flash from the list, saving, and that would solve the problem.

However the "XProtect.meta.plist" and "XProtect.plist" files don't exist in OS X 10.6.8, as that part of the way the System works was only added with later versions of OS X.

If I could only find where, in 10.6.8, this "blacklist" resides, then I could edit it to remove Adobe Flash from the blacklist, which would unblock the plugin. Or so I hope. Maybe I'm barking up the wrong tree -- but if someone on the Apple Discussion boards has some expertise on the 10.6.8 system file structure and knows where the blacklist resides (if at all), then maybe that would be the simplest and most direct solution.