Installing Adobe Flash Player 10.0.42 Plugin for Firefox 3.5.7

I currently have Firefox 3.5.7 installed and am trying to access a site that requires the current version of Adobe Flash Player (10.0.42). When I download and install it, the website still doesn't recognize flash player being installed.

I go to Adobe.com, make sure I am downloading the one for WinXP/Firefox and install it, then it says that it is successfully installed. However, when I try to access the site, and it says that the current version of flash player is not installed, with a link to the adobe site to download the latest version (which I already did).

I have tried uninstalling the flash player, from both Windows and Adobe's uninstaller, and reinstalling with no success. I have even tried uninstalling/reinstalling Firefox, still nothing. For fun, I tried updating IE, and it works fine, but I REALLY don't like IE.

Another note: when I uninstall Flash Player, it doesn't remove it from my machine (add/remove program list), even when Windows asks, "Adobe ... is already uninstalled, would you like to remove it from the list?" Additionally, when I go to Adobe's Flash Player version tester site, it reports that IE is running version 10.0.42, but when I access it with FF, it shows a link to download the latest Adobe FP.