Flash Player in Firefox Problem

I am at wits end! I have an iMac with OS 10.5.8, with Safari and Firefox browsers installed. I needed to update the Firefox browser and also the Flash player. No video plays now. I get messages on You Tube about "some plugins required by this page have been blocked for your protection" and on other sites, "install Adobe Flash Player". I have tried uninstalling the Flash player and reinstalling. Nothing works. Can someone help? Or should I just trash Firefox and download another browser?

Is your iMac powerPC or intel?
In Firefox, go to the tools menu >Add-ons >Plugins andtell us what it says for version of Shockwave Flash (or Adobe Flash).

Did you get the Flash installer (.dmg) file directly from Adobe.com?

Intel ... Shockwave flash is marked disabled due to security issues. As far as I know the installer came from Adobe.

If it's disabled it's because it's an older version. Firefox does this. Go to Adobe and install the latest version.
Should be 11.3.300.257

The version you specify is for a later operating system than mine; Adobe specifies the version I downloaded. It's 10.3.183.20.

I hadn't noticed that before (lower version for 10.5). Time to upgrade your OS X - 10.6 is only $29 from Apple or Amazon.