This is totally fine, and great if want perfect anonymity. If you’re ok with the bot being tied back to your real account through several abstraction layers, you can create an app on your main account (where you probably already have your phone number tied), and then authenticate you bot against that app.
Firefox is also releasing support for subresource integrity, and the “crossorigin” parameter will let you strip cookies automatically. https://hacks.mozilla.org/2015/09/subresource-integrity-in-firefox-43
Separate domains are still recommended, but this is a really interesting feature that provides some of the benefits.