[XBL has been deprecated](https://mozilla.github.io/firefox-browser-architecture/text/0007-xbl-design-review-packet.html) and is [being replaced by WebComponents](https://mozilla.github.io/firefox-browser-architecture/text/0004-xbl-web-components.html), with ongoing work on this being tracked by [bug 1397874](https://bugzilla.mozilla.org/show_bug.cgi?id=1397874 "NEW - [meta] De-XBL") and [Are We XBL Still?](https://arewexblstill.com/). This will break everything in [`/classic/xml/`](https://github.com/Aris-t2/CustomCSSforFx/tree/master/classic/xml).
XBL has been deprecated and is being replaced by WebComponents, with ongoing work on this being tracked by bug 1397874 and Are We XBL Still?.
This will break everything in
/classic/xml/.