Can work on almost any webcomic/manga page, preloads 5 or more pages ahead (or behind), navigates via ajax for instant-page-change, lets you use the keyboard, remembers your progress, and it's relatively easy to add new sites
Now with the newest firefox update (39) the 2nd issue has been resolved =)
Problem which ruins the reading experience
The script itself is a great, tyvm for making it, but sadly some problems make it uncomfortable to use:
After Pageload / Full Image
This isnt that much of a problem since you can just add borders to get the full image, tho it still is weird
How they appear / How it should be without any blurryness
This can be fixed by zooming in/out till the blurryness disappears, but then you have to do it every few pages (i assume when the image change in size)