The "Add bookmark" page has a link at the bottom to a "Bookmark in Confluence" bookmarklet, whose contents is:
javascript:javascript:var title='';var desc='';url=document.URL;if(document.getSelection){desc=document.getSelection();}else{if(window.getSelection){desc=window.getSelection();}else{if(document.selection){desc=document.selection.createRange().text;}}};title=encodeURIComponent(document.title);location.href='http://extranet.atlassian.com/plugins/socialbookmarking/updatebookmark.action?url='encodeURIComponent(url)'&title='title'&description='+encodeURIComponent(desc)
When I click this and bookmark a page, the bookmark apparently gets created, but I am then redirected to:
http://www.atlassian.com/atlassian-public-pom/confluence-plugin-base/socialbookmarking
which returns a 404. The plugin ought to be redirecting me to the bookmarked page.