Never neen to Facebook, so not sure I can help, but PPC Macs generally have problems with FB due to our outdated Flash version.
The last really supported Flash for PPC was 10.1.102.64, but if it's for like Facebook or such, people have been fooling FB to think they have a leter version installed.
Texas Mac Man's Flash hack/post...
Flash player 11.1 hack on PowerPC - https://discussions.apple.com/message/16990862
Might be later ones around also... saw 11.3 I think.
(If you are running a PPC Mac with Flash Player 10.1.102.64 and are having problems with watching videos on FaceBook or other sites, contributor Texas Mac Man suggests the following solution which fools the site into thinking that you are running the latest version:)
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.
You should also consider the Shockwave Player, which displays Web content that has been created by Adobe Director, much used for multimedia: For PPC Macs: http://get.adobe.com/shockwave/
See in each Browser which version of Flash it thinks it has...