1820588 - Investigate adding MozHTMLElement.insertCssIfNeeded

Status: NEW

(Toolkit :: UI Widgets, task)

Description

[Hanna Jones [:hjones]]

In some cases we create custom elements that handle adding their own styles to the document/ShadowRoot. When we do this, logic needs to be added to ensure that each instance of a custom element doesn't re-append the same stylesheet. If we're finding this is a commonly repeated pattern we may want to create a method to support this in a universal way - along the same lines as MozXULElement.insertFTLIfNeeded.