You will need to install a user script manager extension to install this script.
The script keeps separate lists for artists' own works (http://www.pixiv.net/member_illust.php?id=######) and images they've responded to (http://www.pixiv.net/response.php?mode=all&id=######). These can be added/removed/cleared using appended links from those pages as well as member profiles. Works pages can also be added from Danbooru artist entries using the links that appear next to member profile links; response pages can only be added on Pixiv.
On most Danbooru/Pixiv pages, a link near the top-right corner will send you to a random link of either type (favoring works pages by default), selected from either the links that haven't been cleared or (if all links are cleared) from the links cleared a minimum number of days ago (specified at the top of the script).
If the Greasemonkey API (GM_setValue/GM_getValue) is not available, a single pair of lists can't be maintained between the two sites, so the Danbooru side is automatically disabled to prevent confusion.