What does Command-B do in Safari? (without the shift)

Hello.

I'm on my Mac Mini M1, Big Sur 11.2.1using safari and I accidentally hit "command-b", thinking it would open the bookmarks menu, which is accessible via the "command-shift-b" command.

After having hit command-b, the website I was in opens some kind of a debug version of itself in a new tab.

I searched the web for this safari shortcut, but I cannot find any mention of it, not even in the official Apple list of shortcuts for the browser.

I was wondering if you knew what this specific shortcuts does and if you could kindly test it yourself, thank you very much

Cheers.