The lightbox is currently not loading for me for images attached to threads or resources.
No javascript errors. No issue on my own site. Not a caching issue as I've just loaded XenForo.com for the first ever time on Safari and the problem is there too.
My window is as tall as it can be on a 1280 x 800 display (13" Mac Book Pro - non retina) but I have a download sitting in my download bar which shrinks the window by about 30px or so in Chrome.
In Safari I forgot I wasn't logged in . I get the lightbox logged in on Safari.
Can mark as Not a Bug but would be ideal if the limit could take into account a touch smaller screen size as 13" displays are not uncommon.