I didn’t mind the new layout so much until I realized posting anything was a mess.
I use Firefox so didn’t bother with the Chrome trick floating around, but then realized I might be able to copy whatever trick over. And yes, the Chrome trick was just to switch the user agent (essentially the browser) to IE. There are already a lot of extensions to do that for Firefox.
I picked UAControl because it lets you control the user agents for individual sites and I only wanted to change it for Tumblr, nothing else. Once you have it installed, add a new site “http://www.tumblr.com” and then toggle Custom and put:
Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
Once you do that (and I’ve noticed this on both Chrome and Firefox, not sure how common it is), clicking on the Edit and Reblog buttons from posts doesn’t seem to be working, maybe I had other extensions messing with it. So I wrote up a tiny little script that’ll forward you to the right page.
Edited: Fixed the Chrome trick link above, it was going to a deleted post. What you do is pick IE9 after the add-on.
Also, the way to access the UAControl options in Firefox is to go to Tools > Add-ons and then options for UAControl.
And lastly, you’ll need the Greasemonkey extension for Firefox to use the script I wrote but you can add it directly on Chrome. (And by directly, I mean, you don’t need the Greasemonkey extension, but because of Chrome’s restrictions on third-party content, you may have to go through the extra steps of first downloading the script to your computer, and then dragging it onto the Chrome Add-ons tab.)
Edited again: Firefox and Chrome both now seem fine without the Greasemonkey script. Repeat, you should be able to get by with just switching the user agent. You may need to restart the browser, but the script is unnecessary.