When implementing an older version of resp_img that requires multiple Image Styles for each "style" to display images in various sizes for various devices, a serious number of Image Styles are required. As this number of Image Styles grow, Lightbox2 updates to add options for all combinations of Image Styles and this gets to a point where the Manage Display page takes forever to load, and forever to modify the order and layout region location of each field, as well as saving the Manage Display form.
It took me quite a while to figure out what was making this simple process soooooooo slow and once I disabled lightbox2 everything went back to a relatively speedy reaction. Before disabling it, it would require me to hold down the left-click for at least 2 minutes while moving a form field, just for it to display the intended move, even before letting go to make the move official and allow AJAX to do it's thing.
Since this is the case, I feel this makes lightbox2 unusable and recommend it move all those settings into the gear cog icon/Settings for each form field display instead of the dropdown. As I'm using Colorbox now, lightbox2 isn't really needed but I did find lightbox2 to have a better user interface without custom CSS and/or scripting.
Cue the funeral trumpets and bury the 609+ issues in the issue queue along with the module or update it since this is a major development time issue whether you're using resp_img or not.