direct link to all gelbooru images in search results+
On page with thumbnails of all images makes them link to actual fullsize image files + original links via right click
Update: as it is no longer possible to get direct image URLs from image list, I just added support for gelbooru into Handy Just Image script https://greasyfork.org/ru/scripts/109-handy-image - it is more comfortable to use, try it instead.
it means that THIS SCRIPT IS OBSOLETE, please use above instead if something does work right.
