Overlaying built-in tree with custom columns

I have a XUL extension which overlays the Saved Logins window, putting custom columns into the tree therein. The way I’ve made it work is to replace methods of the treeview object, such as getCellText(). (Yes, I know it’s a bit of a hack, but there seemed to be no other way.) But recently, this stopped working. The “view” property now returns an XPCWrappedNative_NoHelper object. Attempts to assign to properties have no effect, and there is no “wrappedJSObject” property.

At this point, I’m not sure what I can do. Is it time to give up on it already, or is there some other way I’m not aware of? I mean, I know XUL extensions are on their way out, anyway, but it would be nice to keep features going as long as possible.

That’s going to be sometime soon this year. I wouldn’t waste my time and effort.

Here’s the current timeline for legacy add-on removal:
https://blog.mozilla.org/addons/2017/02/16/the-road-to-firefox-57-compatibility-milestones/