This is a very handy addon! Only thing I would recommend would be better documentation and commenting of the source code, and it's not immediately obvious what those arrow buttons are in the top right (maybe they could have title= attribute set to an explanation).
This add-on saved me possibly hours of work when trying to find what had changed on a site I was working on. The background had randomly re-sized and the text had spaced out and there was nothing in the editor that had changed. I popped up the new preview link and the old preview link and brought up the difference in the html and had the site back to normal within a couple minutes. Awesome Add-On! Thanks So Much!
I was very pleased to find this add-on but in practice it made me mad! The output suggested there were attribute in the tags like Class="" ! In the source of my FireFox 3.6.6 (under Windows 7) browser I never found those attribites! It is really a pity!
In my project, most of the time I need to print difference between my developed code vs older version. We are not using beyond compare. I would like to add any add on which will compare content comparison rather HTML comparison.
Hey, great stuff! It would be handy if along with the line selection there were a subselection showing exactly what in the line had changed. Generally not an issue with short lines, but gets hard to see what's going on when developers don't bother with cosmetics like line breaks :)
Also, a running page view of where the diffs occur down a long page would be great.
Great extension - ALMOST exactly what I was looking for. If it could also compare the output (pages as seen in a browser) in addition to comparing the code, I'd be in heaven. I don't know much about building extensions, so I can't tell if such option would be easy to implement, but I sure could use it... ;)