"Upload to dropbox" fails to enable with firefox opening tabs in the background

[tstenner]

When Firefox is configured to open tabs in the background, the "Export Data to Dropbox" checkbox gets checked immediately, but even after switching to Firefox and authorizing the app it doesn't persist, i.e. after switching to the main settings menu and returning into the upload menu, it's disabled again.

Configuring Firefox to immediately launch when an app requests to open a tab fixes this, but it isn't obvious.