The Firefox version of cairo unconditionally turns on a "buggy-repeat"
fallback in Cairo that does tiled repeating images by grabbing everything
to the client, doing the repeat in software, then pushing the result
back. This can be extremely slow.

(It may be even slower with the kernel modesetting drivers that we are using in Fedora 10, but it is always going to be really slow.)

It's not completely clear what X server bug was being worked around, but
it doesn't seem to be present in recent X servers, like the Fedora X
server. Quoting from IRC:

<vlad_> try running with MOZ_CAIRO_NO_BUGGY_REPEAT=1 in the environment
<vlad_> we unconditionally force buggy repeat handling because we couldn't figure out a good heuristic to determine which x servers/drivers had the buggy code
<vlad_> so when we last looked at it, the bug existed in 1.3.0.0 and seemed to be gone in at least xorg 1.4.99.901
<vlad_> so what we could do is disable that forcing for > 1.4 (or 1.5, whatever the latest is)
<vlad_> otaylor: filed https://bugzilla.mozilla.org/show_bug.cgi?id=456467

We should make sure that we have this fallback off for F10, either by pulling an upstream patch, by setting the environment variable, or by some either means.

One test case of this is header of http://www.smh.com.au , but it probably will be triggered on many web pages.