Fancybox is loading well and everything opens as I want it to, but the issue occurs in the background-- it\'s visible (and disturbing) that my entire page shifts exactly 8 pixel
You are facing that problem for scrollbar! just trace the scrollbar width and use that width as '.fancybox-lock's 'margin-right'. for example,
.fancybox-lock{ margin-right: [your calculated width] !important; }
This will solve your problem for sure, because i also had that problem once.