Prevent built-in prompts in xul

Question

I have an application that loads a web page in the browser and saves it to custom local folder (images, html, css). In the process the "src" attribute of images (in html) and "background-url" property (in css) need to be changed to reflect the locally saved files rather than the original ones. This generates extra web traffic as changing them forces the browser to download the files from modified locations (the browser does this by resolving the uri of the page with the value of element's "src" attribute - the same for "background-url" property ) and as a result, it generates lots of 404 Not Found requests.

I'm using nsIIOService interface to go offline before saving the page (the page is fully loaded and all network activity so far has been stopped) and then back online after the saving is complete. But then the browser displays an alert box "This document cannot be displayed while offline. To go online, uncheck Work Offline from the File menu." whenever I try to change the aforementioned attributes/properties.

Is there any way to prevent such message from appearing or to make the browser not validate the images because of modified "src" values?

I tried to use DOMWillOpenModalDialog on both the browser and the xul application window, but it seems it's of no use - the dialog still appears. The application is not an user application, so it's difficult when such "built-in" messages appear.

Answer 1

Use preventDefault to stop the modal dialog:

document.getElementById(‘content’).contentWindow.addEventListener(‘DOMWillOpenModalDialog’,function(e){ e.preventDefault(); }, true);

As an alternative, try using disablePrivilege, sandbox, redefining the prompt service, or overriding window.alert.