It would be good if the extension remembered the options, and wasn't randomly affecting all tumblr tabs. (why would someone want to turn all tumblr tabs to an archive anyway?: with many tabs, it will affect firefox & CPU perfs a lot).
Also, it shouldn't affect the dashboard or images/media opened, whatever the settings are.
This extension is a good idea, but needs a serious polishing.
Also, could we get the link to the source code?
Keep on improving, developper, this could be a cool extension. I'll change my review accordingly ;)