First, trusted testers may not be the right deployment mechanism for you. Based on what you shared so far it sounds like you are relatively early and need to quickly iterate. For better or worse, the Chrome Web Store does not serve that scenario very well.
Since you're prototyping with colleagues, another solution you might want to consider is setting up a network drive and having everyone load the unpacked extension from that location. You could even combine this with some simple polling logic in the extension to check if it has the latest version and to use
chrome.runtime.reload when a new version is detected. It's not elegant, but it should work. Or if not a shared drive, perhaps use rsync to push out changes? You could even combine this with the
--load-extension command line flag on your Chrom(e|ium) shortcuts to load the unpacked extension.
An alternative (and significantly more complicated) route is to self-host your extension on your own web servers and to use enterprise policies to force install the development version on the desired devices. This would leverage Chrome's automatic update flow, but it requires a lot more work to update, package, and deploy (or at least set up that process). Our docs on this topic aren't great, but at the moment I think the
Managing Extensions in your Enterprise whitepaper is probably the single best resource. You'll most likely want to focus on the "Create your own on-premises web store" section.
Second, based on the information you've provided so far you may not actually <all_urls>. If you only want to take screenshots in direct response to the user action such as clicking the browser action or invoking a keyboard shortcut, you can potentially use the
activeTab permission.
Cheers,
Simeon - @dotproto
Chrome Extensions DevRel