I have met many older mac users with the same complaint, yet every single case was user error. Tiger is only has good as its update's (well i take that back Tiger is awesome), Flash needs its love as well. TO Fix your Problem of Flash viewing follow the steps bellow:
Upgrade to Tiger (Flash will work on Panther with no sweat, but the Grrrr of Tiger is not something to be without), after completing all of your Apple software updates follow up by upgrading your plug-in's; flash, realplayer, the foul WMP....
If for some reason you still are having some difficulties spotlight flash and see if the newest version made it to your safari plug-in's folder under library (You have two or more Library folders with Internet Plug-in's make sure it are under your current user Library.
If you still can't figure it out back-up your system and bring it to a Apple Store.
I have been designing Flash projects on a Mac more than a day or so,::ha:: , Flash works with perfect speed and detail on my machines and those of every Mac Flash designer I work with day-to-day and work with.
PS
If you insist on using Mozilla don't use the Microsoft looking FireFox why muck the look of your mac, use
www.caminobrowser.org
Or
Try;
Omniweb