execCommand[0] has a "paste" option, which pastes the content of the clipboard at the current insertion point. This allows for "reading" of the clipboard.

This article doesn't mention "paste" specifically, but the footnote[1] in the "paste" section says:

"[1] Before Firefox 41, clipboard capability needed to be enabled in the user.js preference file. See A brief guide to Mozilla preferences for more information. In Firefox 41 and later, clipboard capability are enabled by default in any event handler that is able to pop-up a window (semi-trusted scripts)."

This footnote is not attached to any other command, and thus "paste" is singled out. This could just be a documentation error, or maybe they didn't want to highlight that paste was also being enabled. I don't have a FF v41 in order to test what the actual behavior is.

[0] - https://developer.mozilla.org/en-US/docs/Web/API/Document/ex...