Affecting @-moz-document support will be dropped

Published: | Categories: CSS Privacy & Security


The @-moz-document rule will no longer be available from Web content since it could be used by attackers for CSS injection to steal private data in the URL of third-party sites. Firefox users are still able to use this rule in their user stylesheet to personalize the browsing experience.

Update: An earlier draft of this document said the change was made with Firefox 44, but the patch was not merged to that version due to a layout compatibility issue on the <fieldset> element. The bug is expected to be solved soon.

Update 2: The at-rule support has been removed again from Nightly and early Beta as of Firefox 59. It will soon be completely dropped.

Update 3: Telegram and YouTube are known to be broken due to this change.