I've noticed a problem when scrolling on sites with tiled background
images in my iceweasel recently. It's hard to explain, but let's try
some ASCII art.
Let's say there's a page with a tiled background image that looks like
this (substituting punctuation for coloured pixels):
.......#
.....###
...#####
.#######
When tiled to cover the entire background of the page, it naturally
looks like this:
.......#.......#.......#.......#.......#.......#.......#......
.....###.....###.....###.....###.....###.....###.....###.....#
...#####...#####...#####...#####...#####...#####...#####...###
.#######.#######.#######.#######.#######.#######.#######.#####
.......#.......#.......#.......#.......#.......#.......#......
.....###.....###.....###.....###.....###.....###.....###.....#
...#####...#####...#####...#####...#####...#####...#####...###
.#######.#######.#######.#######.#######.#######.#######.#####
However, if the page content is too wide for the window, and I scroll
one pixel to the left, I'd expect to see:
......#.......#.......#.......#.......#.......#.......#.......
....###.....###.....###.....###.....###.....###.....###.....##
..#####...#####...#####...#####...#####...#####...#####...####
#######.#######.#######.#######.#######.#######.#######.######
......#.......#.......#.......#.......#.......#.......#.......
....###.....###.....###.....###.....###.....###.....###.....##
..#####...#####...#####...#####...#####...#####...#####...####
#######.#######.#######.#######.#######.#######.#######.######
(that is, the left-most column of pixels is no longer visible, and a new
column of pixels has scrolled into view on the right)
What I actually see is more like this:
......#......#......#......#......#......#......#.....#.....#.
....###....###....###....###....###....###....###....##....##.
..#####..#####..#####..#####..#####..#####..#####..####..####.
##############################################################
......#......#......#......#......#......#......#.....#.....#.
....###....###....###....###....###....###....###....##....##.
..#####..#####..#####..#####..#####..#####..#####..####..####.
##############################################################
...and if I scroll three pixels further, I see:
...#...#...#...#...#...#...#...#...#...#...#...#...#...#...#..
.###.###.###.###.###.###.###.###.###.###.###.###.###.###.###.#
##############################################################
##############################################################
...#...#...#...#...#...#...#...#...#...#...#...#...#...#...#..
.###.###.###.###.###.###.###.###.###.###.###.###.###.###.###.#
##############################################################
##############################################################
...which is to say, the left most pixels are being clipped off, and it's
the narrower, post-clip image that's being tiled to the width of the
viewport.
After scrolling a distance approximately equal to the relevant
dimension of the background image, Iceweasel comes to its senses and
starts painting the background in the same way every other browser does.
I've created a (fairly) minimal test-case here:
http://jsfiddle.net/QsCAs/1/
I can reproduce the problem when starting Firefox like this:
$ rm -rf /tmp/test-profile/
$ mkdir /tmp/test-profile
$ iceweasel -no-remote -profile /tmp/test-profile/ \
http://jsfiddle.net/QsCAs/1/
My iceweasel package is installed from the 'iceweasel-aurora' repo
advertised on mozilla.debian.net, and calls itself version
"22.0~a2+20130510004016-1".
I downloaded a Firefox Aurora tarball from ftp.mozilla.org with the same
datestamp (it calls itself "22.0a2 (2013-05-10)") and it does not
exhibit the same problem.
I'm using Debian Testing, freshly-updated, on x86_64.
Is there any other information I can provide? I would have filed
a proper bug, but this Aurora package isn't an official part of the
Debian archive.
Tim.