If you have this dialog in Firefox, you can use PolicyPak to specify Allow or Block Plugin.

If the plug in you want to allow is Java, you can add one line to the PERMISSIONS section in the PolicyPak Application Settings Manager Firefox Pak.

website.com, plugin:java, allow

Note:  You might also need to add these lines as well, if adding the one line above doesn’t work. It depends on the version of Firefox you have installed. Older versions require these lines:

website.com, plugin-vulnerable:npdeployjava, allow
website.com, plugin:npdeployjava, allow

However, if the plug in you wantis another plug-in and not Java, then you need to learn the plug in name in the database. So, start out on your own machine and use Firefox to specify the ALLOW AND REMEMBER permission or BLOCK PLUGIN permission as seen here.

Once this is done, you need to figure out what plug-in was just affected. The way to do this would be to use a tool called SQLLite Browser found here:  www.sqlitebrowser.org

Open the table / file moz_perms (on FF 42 and newer) or moz_hosts (on FF 41 and older) which will be in the C:\Users\AppData\Roaming\MozillaFilrefox\Profiles\permissions.sqllite file.

Discover the name of the plug-in you just approved like what’s seen in this example. In this example, it’s still plugin:java. But in your case, it could be something else.

Now that you know that, you can use PolicyPak Application Settings Manager and the Firefox Pak to set this permission to Allow or Block.