The essence of the article:
The discussions, visible in Mozilla’s Phabricator revision D277804 and a linked GNOME gsettings-desktop-schemas merge request, focus on disabling the traditional primary selection paste by default.
Mozilla proposes changing the default behavior of the Firefox browser on Unix builds so that pressing the middle mouse button no longer pastes text by default.
The functionality will be there and can be enabled. The reasoning:
The author of the revision frames the current behavior as a source of confusion and accidental pastes, especially when users press the middle button without expecting the clipboard contents to be inserted into text fields.