browser_webconsole_select_all.js is going to start failing with bug 1753177 landing. We'll need to figure out what we want to do with this test and the functionality it is using.

I think we could change what the test really does, and instead of checking that the text is selected, maybe test what happens when the user select all and then want to copy the selection.
As you suggested at some point, I think we could listen to the copy event, check if the text selection range includes the first and the last message, and if so, trigger the Copy all messages action that will handle this (see https://phabricator.services.mozilla.com/D142189)