Settings being reset is kind of expected with a rewrite like this. Should go through and reconfirm your "open popup" settings, etc.

Edit, Resolved: If you get a blank page instead of Tumblr sign-in, disable other add-ons to be able to log in, then you can re-enable them.

One gripe: I can't pick a sideblog on the posting pop-up anymore -- have to set the blog on the add-on icon before right-click to reblog. A few more steps, but nothing horrible.