Flash Player version 10.1.102.64 is the last version available to PPC Mac users. However, this Flash version won't work for many videos on Facebook, YouTube and other sites. Adobe's latest version, 11.x or later, is only for Intel Macs. Adobe will not provide a newer Flash version for PPC Macs.
The message requesting that you download Adobe Flash Player takes you to Flash Player requiring an Intel processor. Doesn't work on a PowerPC processor. I found a hack, installed it & it works with Firefox, TenFourFox & Safari. (Havent tested on Chrome)
Download this http://www.steelbin.com/FPforFBPPC.zip to your desktop, unzip it, and replace the current Flash Player plug-in which is in your main/Library/Internet Plug-Ins folder, (not the user Library). Save the old one just in case this one doesn't work.
Hack Allows PowerPC Macs to Access Flash 11 Content
http://lowendmac.com/ed/royal/12sr/flash-11-and-powerpc.html
If you use the modern browser TenFourFox, it has plugins disabled by default, meaning Flash is not there. This can be enabled easily by doing the following: In the TenFourFox address bar type about:config and press Enter/Return. Look for tenfourfox.plugins.enabled (currently set to false) and set it to true (double click the line to change). This will enable Flash. The developers advise against this as it may cause an instability issue, but if you need Flash then you have no option.
Cheers, Tom 😉