Hi!A browser extension named "Enhanced iFrame Protection", which has this github repo: https://github.com/odacavo/enhanced-iframe-protection, gives the user a verbose warning when detecting iframe elements.
The warning is showed to warn the user about a potential security risk. This seems to be a logical feature Mozilla should have.
If implemented, the user should have the ability to e.g. disable/enable iframes in settings in the "Privacy & Security" tab.
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No more iframes ... execpt when you click the toolbar button.
Hope it helps.
As a footnote, you might be okay with iframes from the same host name or related host name. By that I mean, for example, if you are browsing on www.example.com, you might be okay with frames from www.example.com or images.example.com. On the other hand, you might want a warning for a frame from www.youtube-embed.com.