Rated 4 out of 5 stars
It's good, but, I think it's fair to assume that most people downloaded this to restore the old picture display, considering the name of the add-on.
However, we have to manually go into add-ons > Extensions and set this to center the image and have a gray background. That doesn't make any sense; the default settings should be the old style. I don't see how that's even debatable.
I love customization but your default installed settings being the current inferior settings just causes the user to spend time customizing what they expected your add-on to do by default.
Also, it doesn't work on SVGs at all :(
EDIT: Ohhh okay. I looked it up and looks like the "gray centered" display method started with Firefox 11. I've always loved this display method because I think it's superior in all ways to the top-left white background display method. It's been a long time since I was from Firefox 3.x.x.x to the newer quickly-increasing-version-numbers phase (their stupid idea to compete with Chrome) so I did not recall that it didn't appear until 11.
I think we have different ideas of what "old" means. The title refers to the style used from Phoenix through to Firefox 10.0 (that is, the browser's default background color without centering).
(It's not the clearest of names, especially after the scope creep that led to all the various options, but there it is.)
And yeah, no SVG support. Check my response a few reviews back for the reasons for that.