In Bug 2008041, the disabled attribute was turned into an html-style boolean attribute,
meaning that its presence only indicates that the element is disabled, regardless of the
attribute value.
The context menu entries in the Style Editor were still assigned true/false values,
which means that they were now always considered disabled.
The test covering the context menu behavior didn't catch that because they're using
(the recommended) activateItem method, which doesn't check the disabled attribute
before calling the event listeners.
This patch fixes the disabled attributes and adapt the existing tests.
Differential Revision: https://phabricator.services.mozilla.com/D301052
Nicolas Chevobbe
18af692564