rwp

This line of jQuery will find the span with "Back" and replaces it with "Tilbake"
$( "span:contains('Back')" ).html("Tilbake")

Great!

Alright, so I poked around a bit more. It's hard to see whats really going on without being logged into your page, but something about it is set up differently than mine.
Lets start with the basics, is it a gallery block?
If so, do your settings look like this?

.gallery-fullscreen-slideshow-item-img{ transition: opacity 1600ms ease-in-out !important; -webkit-transition: opacity 1600ms ease-in-out !important; -ms-transition: opacity 1600ms ease-in-out !important; -moz-transition: opacity 1600ms ease-in-out !important; -o-transition: opacity 1600ms ease-in-out !important; } .gallery-fullscreen-slideshow[data-transition="fade"] .gallery-fullscreen-slideshow-item[data-active="true"] .gallery-fullscreen-slideshow-item-src{ transition: opacity 1400ms ease-in-out !important; -webkit-transition: opacity 1400ms ease-in-out !important; -ms-transition: opacity 1400ms ease-in-out !important; -moz-transition: opacity 1400ms ease-in-out !important; -o-transition: opacity 1400ms ease-in-out !important; } Currently getting some hiccups with Firefox.  This is on SquareSpaces side of things.  I already spent about 3 hours trying to get this to work, and I don't feel like digging though a million lines of code again.  (The standard transition doesn't work right in Firefox either, its just too fast to notice).
Anyway, this works with every other browser that I tested. I added 1000ms to the default values, I am not sure if the 200ms differences matter much, but I left them. You can probably leave out the importants, and honestly, you don't need the webkits, but I guess if someone is on a very old browser its good to toss them in there.
I will attempt to get this over to SS to see if they can fix the Firefox issue.  It fades sometimes, snaps the next, not sure whats up.