Flash Player Settings

On my Firefox browser, I am trying play Bloons Tower Defense 5, and adjust the graphics settings.  I right click on the game area, and the settings box appears, but from this point I can not close the settings box.  I can not even select any options in the box.

I can again right click and select from the next menu, (where I need to go to set the graphics level), but other than close out the game, I can not do anything else.

I only have problems with Firefox.  Chrome and Edge work fine, and I have not tried IE, I would just rather play on Firefox if this can be fixed.

Please help.

Thank you.

Edit  I forgot to mention that I am  using Win10