2.2.32 [HTML] Section 16.4.1, The NOFRAMES element
The specification states:
The NOFRAMES element specifies content that should be displayed only by user agents that do not support frames or are configured not to display frames. User agents that support frames must only display the contents of a NOFRAMES declaration when configured not to display frames. User agents that do not support frames must display the contents of NOFRAMES in any case.
All Document Modes (All Versions)
The content of the NOFRAMES element is ignored when a site is a member of the Restricted sites zone.