JavaScript Animated. How To Implement jQuery "Magnific Popup" Lightbox Plugin

Hello! The code works, but for some reason the effect does not work when I open site in browser window (firefox). I did try a different browser but same thing. I am using TextWrangler to write my website. I also have Dreamweaver and I tried that too, but for some reason the plugin won't work...so then I used CodePen to see if code works and it does! Is there any tips or hints to why the plugin does not show when previewed in Firefox.

this doesnt work

not clear at all

very helpful. i thought id never figure out how to use this plugin. thanks