Missing e: No Ads!
A handful of people have mentioned seeing ads injected into the Tumblr dashboard (not put there by Tumblr, itself).
Let me assure you that Missing e does not place any ads on any site whatsoever. I firmly believe that doing so without user permission is dishonest and inappropriate.
If you are seeing ad banners and the like on Tumblr, try disabling other extensions and add-ons you have installed in case any of those are causing it.
You should also make sure to download Missing e and its updates from official sources: missing-e.com, the Chrome Web Store or the Firefox Add-Ons site.
Note that the Missing e blog page and website do have banner ads to help support development.