Thanks for the post, but to be clear, I'm on Mountain Lion, not Snow Leopard. I'll look into the version of Flash Player and the plug-in that my co-worker is using and update them and see if that helps.
I'm also checking out the articles in the "More Like This" sidebar. Glad to see I'm not the only one encountering this, so I know it should be solvable.
OS X 10.8.4 Mountain Lion
Latest Flash Player Plug-in version is 11.8.800.168
1. System Preferences > Other/ Flash Player > Advanced > Delete All
Press the "Delete All" button
Install Adobe Flash Player.
Restart computer. Relaunch Safari.
2. Enable Plug-ins
Safari > Preferences > Security
Internet Plug-ins > "Allow all other plug-ins
Same thing happened to me when I updated to Yosemite. Mine in particular was with the Google Music app.
In tinkering with the stuff other people have said I came across this:
System Preferences --> Flash Player --> Advanced --> Check Now
Prompted me to install an update for Flash, then a quick restart and I'm back to normal. Hope this helps!
For those who have downloaded the Adobe flashplayer, and thought it would install on it's own, add 1 more step:
Go to the search box on your Mac (or however you search on it) my search box is next to the time display.
Type in downloads and folders should pop up. Click the one that shows your username out to the left. Find the flashplayer and double click on it.
Follow the directions and install Adobe.
This is the most important step of all.
You may not have to download it, it's possible that it was already on your device from a previous update, these steps should have you well on your way.