Legacy Thunderbird add-on: 'database' property of XUL <menu> element is undefined

I’m working on making my legacy XUL+XPCOM add-on for Thunderbird compatible with version 59. The add-on uses RDF for storing user-generated data, and RDF templates are used to dynamically generate menus and trees in the UI from the RDF datasource.

When I started up Thunderbird 59.0 beta with my add-on installed, I’m getting the following error in the console:

TypeError: aMenu.database is undefined

…where aMenu is the XUL <menu> element that has both the datasources and ref attributes set.

There’s a similar error when initializing a window from my add-on containing an XUL <tree> element whose tree nodes are dynamically generated from an RDF template. In this case, the error is that “tree.builder is undefined.”

This error doesn’t occur if I’m running Thunderbird 52.7.0, the current stable release.

I understand there has been a lot of changes in Thunderbird recently, with many things changed or removed. What has happened to RDF templates in XUL; have they been dropped as well?

XUL templates have been removed, see https://bugzilla.mozilla.org/show_bug.cgi?id=1425356

Thanks for confirming.