The HTML Standard defines User Involvement. This is being referenced in the Text Fragments spec to determine if a text directive is allowed to be scrolled to. Gecko currently does not implement User Involvement.

Tagging this as "see also" instead of "blocks" for Bug 1753933 and Bug 1777171.

User involvement as defined in the spec is not implemented in Gecko yet.
Therefore, the changes introduced in Bug 1888756 disallowed scrolling to text directives if the load was triggered by the user, eg. by pasting a link with a text fragment into the url bar.

This patch checks if the triggering principal of the load is the system principal.
This is equivalent to the "browser UI" value of user involvement.

Here is a try run, in which this patch is based off of Bug 1888756 (which at this point of time is only in autoland, not in central).

(Let's use bug 1904773 for the makeshift solution and keep this one for a potential real implementation of user involvement.)

The attached patch switches the implementation of user involvement in Text Fragments from checking the triggering principal directly to using the user involvement flag, which is introduced in Bug 1942630.
At the moment this change makes a test fail because the logic how to set the user involvement has not been implemented yet (hence the WIP status).