Firefox extension - How to display an html block that overlaps the browser window?

Question

I'd like to have my firefox extension display a block of html that overlaps the users browser window. I can currently do this by having some JS that inserts html into the DOM of the page, but I'd like the html to be displayed at a higher level within the browser so that the block remains if the user browses to a new page or switches tabs. Is this possible?

Answer 1

You should take a look at the XUL PopupGuide. Popups can be used for elements floating above the user-interface.

I think Panels, a special type of XUL popup, are what you are looking for. The panel itself is XUL and not HTML, but inside the panel you can safely mix both or just use HTML if you want to.

Cheers.