I will not discuss here right now the big image of the message sent a few weeks ago (although my company is deeply, very deeply worried about it) but I would like instead to dive into a major technical detail that seems to me left blatantly unresolved: the XUL tree element was introduced to handle very long lists of items with performance. Add-ons touching bookmarks, lists of URLs, list of email adresses, contacts, anti-spam lists, advertisement blocking lists and more all need a performant tree solution.

As far as I am concerned, there is nothing on the html side approaching the performance of the XUL tree for very long lists. Having no replacement for it before the removal of XUL-based add-ons is only a death signal sent to all the add-ons needing the XUL tree, and almost a "we don't care about you" signal sent to the authors of these add-ons. From an ecosystem's point of view, I find it purely suicidal.

So I have a question: what's the plan for the limited number of XUL elements that have no current replacement in html for deep technical reasons?

Update: yes, there are some OSS packages to deal with trees in html, but until the XUL tree is removed from Firefox's UI, how do we deal with it if access to the XUL element is not reachable from add-ons?