That depends on your security software. Usually there will be a panel listing the programs that you have allowed and blocked, and letting you remove it from the list so the program will ask you again. Can you find anything like that?

Note: this panel would be in your security software and not in Firefox.

jscher2000 said

That depends on your security software. Usually there will be a panel listing the programs that you have allowed and blocked, and letting you remove it from the list so the program will ask you again. Can you find anything like that? Note: this panel would be in your security software and not in Firefox.

My Windows Firewall shows a list of the programs that are blocked and allowed, how do I go about removing the program from the list to have it ask me again?

If you are in the Windows Firewall part of the control panel, click "Advanced settings" in the left bar. This should pop up a list with Inbound and Outbound rules. You can check each list for plugin-container.exe. I couldn't find anything in mine.

Are you currently having problems using a plugin, or is this more of a theoretical issue? It would be pretty unusual for plugin-container to need you top open the Firefox for inbound access. I would be suspicious about the content in the container in that case.