The ASSERT(!resource->scriptObject) in InspectorController::addScriptResource() fails when the inspector is open and you navigate away from the inspected document to a document coming from the page cache. To reproduce, using a debug build of TOT: 1) Go to data:text/html,foo 2) In the same window, go to data:text/html,bar 3) Choose Debug > Show Web Inspector 4) In the Safari window, click the Back toolbar button
Attachment 15392 [details] in bug 13250 seems to address this bug.
Fixed in <http://trac.webkit.org/projects/webkit/changeset/24516>.