Print Not Working In Web Browser

I used the window.print() javascript to print one of my slides - a certificate of completion slide. It works fine in the player, but in a browser (Firefox 42.0), the print dialog box doesn't appear. The next trigger fires and returns the user to the results slide. That trigger fires after the print trigger and works as designed in the SL player. Any ideas as to why it wouldn't work when viewed in a web browser? TIA!

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