Here’s an example bookmarklet to open a new case with most of the fields copied from a case you’re currently viewing. To set it up in your browser, create a new bookmark in your bookmarks bar. Set the address / URL of the bookmark to the following, replacing [your FogBugz URL] with the address of your fogbugz installation. Line breaks have been added here for readability. The whole thing should be on one line.

NOTE: If you’re using FogBugz Ocelot, you’ll need to change /default.asp to /f/cases/new after
[your FogBugz URL] below.

javascript:a=function(){var bug=((typeof goBug !== 'undefined'))?goBug:fb.cases.current.bug;
var m = new Date(); m.setHours(16,30,0,0); 
var datestring = m.toDateString(); var timestring = m.toLocaleTimeString();
open('http://[your FogBugz URL]/default.asp?command=new&pg=pgEditBug&
ixProject='+bug.ixProject+'&ixArea='+bug.ixArea+'&ixPersonAssignedTo='
+bug.ixPersonAssignedTo+'&sTitle='+bug.sTitle+'&ixBugParent=' 
+ bug.ixBug + '&sDueDate=' + encodeURI(datestring) + '&sDueTime=' + encodeURI(timestring) 
+ '&sEvent=See%20Case%20' + bug.ixBug + '&sCustomerEmail=' + bug.sCustomerEmail);return;};a()

(Here’s the same text as above on one line in case you just want to copy it):

javascript:a=function(){var bug=((typeof goBug !== 'undefined'))?goBug:fb.cases.current.bug;var m = new Date(); m.setHours(16,30,0,0); var datestring = m.toDateString(); var timestring = m.toLocaleTimeString();open('http://[your FogBugz URL]/default.asp?command=new&pg=pgEditBug&ixProject='+bug.ixProject+'&ixArea='+bug.ixArea+'&ixPersonAssignedTo='+bug.ixPersonAssignedTo+'&sTitle='+bug.sTitle+'&ixBugParent=' + bug.ixBug + '&sDueDate=' + encodeURI(datestring) + '&sDueTime=' + encodeURI(timestring) + '&sEvent=See%20Case%20' + bug.ixBug + '&sCustomerEmail=' + bug.sCustomerEmail);return;};a()

When you view a case and click the bookmarklet, it will open a new case in a new window/tab that’s a clone of the case. It will include “See Case XXX” to link back to the other one. You can remove this from the URL of the bookmarklet if you want. If you click it with some text selected, that text is put in the body of the new case as well.