Slightly complicated question, because ActiveX technology doesn't normally run in Firefox at all. But let me set that aside. If this worked in Firefox 20 but doesn't work in Firefox 21, it may be due to the following change:

Firefox can find plugins in several locations, and most installers add a registry entry pointing to the location, but some do not, relying on an old "shared" plugin folder. Firefox 21 changed the location of that folder, leaving you with two options: (1) move the files yourself, or (2) set Firefox to check for the old location. That second step is described in this article: Windows Media or other plugins stopped working after Firefox update.

Does that get you back up and running on King.com?

I followed the instructions to 'true' the plug in. I still cannot play Crescendo Catcher on King.com games. I can play all the other games. Crescendo won't load. If I use IE, which I totally hate, I can play Crescendo so I believe I have all the software plug ins necessary to play. Any other suggestions? Also, if the 'plug ins' folder in IE has the appropriate information, could it be copied to Firefox? if so into what folder? You don't say in the solution above where or name of folder Firefox 21 changed location.

Have you tried King.con games support for help?

Does the appdir plugins folder even exist?
Program Files/Firefox installation folder/plugins/
Firefox stopped using that folder so long ago that the folder itself doesn't even exist in the Firefox 4.0 + versions. Either the plugin installer has to actually create that folder, or the user needs to create that folder manually and "place" the plugin files in that folder in addition to "toggling" that preference to 'true'.

The IE plugins folder probably doesn't contain the ActiveX plugin that Firefox would use, IE supports ActiveX by default - nothing needs to be installed.

Thank you for responding so quickly. Yes, I contacted King support and they can only suggest that I switch my browser to IE......NOT! I suppose if I really want to play just a few Crescendo once and a while I'll have to use IE to do it. Would love it if Firefox could find a way. Have a great day!

ActiveX is one of the scourges for the Windows world. Mozilla never has and will never support it, as there are "better" and safer ways of doing what ActiveX does in IE. At least Mozilla doesn't actually block ActiveX from running thru Firefox if the user is able to install an ActiveX plugin.

Thank you. I might check around to see if I can find a source; it used to come directly from King when you first joined their game site. King no longer shows it on their support page as a 'plug in'. Again, have a great Thursday!!