This google chrome extension automatically extends functionality on a tumblr site..
Because Tumblr can be used on your own domain I look for clues that identify a tumblr site.
keyboard navigation is the first feature I can think of.
Brings GIFs back to Tumblr blogs/dashboard instead of WEBPs
Allows you to edit your Tumblr themes locally on your computer with your favourite code editor.
Tumblr Pro, get your hat, show your pride.
Post your list of favorite tags on Tumblr in one click.
Post to Tumblr right from your browser toolbar!
A revolutionary way to browse Tumblr photo blogs
Puts timestamps in footers of posts in tumblr dashboard
Adds some visual and functional improvements to sdc.com.
Record how far you scroll on Tumblr
Cascadr | A Tumblr Image Viewer