Sometimes, text in foreign frame is reportedly seen from main frame. The current theory is that we don't stop parsing when restarting navigation at the right time. This is of course highly undesirable, as parsing can have other side effects, possibly up to executing scripts. 6.6.5 The application cache selection algorithm When the application cache selection algorithm algorithm is invoked with a Document document and optionally a manifest URL manifest URL, the user agent must run the first applicable set of steps from the following list: If there is a manifest URL, and document was loaded from an application cache, and the URL of the manifest of that cache's application cache group is not the same as manifest URL * Mark the entry for the resource from which document was taken in the application cache from which it was loaded as foreign. * Restart the current navigation from the top of the navigation algorithm, undoing any changes that were made as part of the initial load (changes can be avoided by ensuring that the step to update the session history with the new page is only ever completed after this application cache selection algorithm is run, though this is not required). See also: http://www.w3.org/Bugs/Public/show_bug.cgi?id=10625 or bug 43328