DevTools copy operations don't work in Firefox

[bvaughn]

Attempting to copy a prop using the new context menu (#17608) prints the following error for Firefox:

Error: Unable to copy. Perhaps it's not available in your browser?

Firefox itself does support document.execCommand('copy') if it's within the context of an event handler, but it looks like this does not include events that originated within an extension.

Looks like this was also an issue for DevTools v3: facebook/react-devtools#843

Under the hood we are using clipboard-js for this.

[zinoviev]

@bvaughn I used to work on facebook/react-devtools#843 - facebook/react-devtools#1037 and as far as I remember it works for both Chrome and Firefox for me. Maybe I totaly worng about firefox, but I would like to check this issue

[bvaughn]

@zinoviev It works under certain conditions, but not one where a click event in the extension tries to run document.execCommand("copy") in the page. I spoke with the Mozilla folks about this issue Friday, and they're at least aware of it. Not sure the exact path forward (although if you'd like to take a look and lend a hand, please do!)

I think in the meanwhile- I'm going to close this issue and roll it into #17681 since a few Firefox folks are also tracking that one.