I have seen this behaviour for many previous versions, and on current,
previous, and some experimental YouTube designs. The symptoms are
similar every time: certain blocks disappear, text gets half-rendered or
doesn't render at all. I've encountered similar issues on some other
websites with a fixed bar at the top of the screen, namely, some themes
for Twitter cause it (sorry, can't find links at this moment).

Mostly it looks like:

http://img163.imageshack.us/img163/3748/20130106180401380x42scr.png

Sometimes the whole page becomes unusable:

http://img29.imageshack.us/img29/720/201301061804361400x735s.png

But if it's scrolled a bit, elements get redrawn again:

http://img189.imageshack.us/img189/1019/201301061805091043x171s.png

However, they may disappear in few seconds again, and I have to scroll
the page back and forth.

 I see the behaviour described in this report with Iceweasel 18 both on Squeeze
and on Wheeze. A vanilla firefox 18 build downloaded from mozilla.org does not
exhibit this behaviour. So it must have to do with Debian specfic modifications.

This behaviour has also appeared fairly recently. IIRC, Iceweasel 17 was not
affected Iceweasel 18.0 was also still fine. Could it be related to the patch
introduced to fix the handling of the language packs?

Johannes

It's probably a libcairo2 issue.

Mike

src:iceweasel has been superseded by src:firefox-esr in version
45.0esr-1 in March 2016. Transitional packages to ease upgrades were
provided in the wheezy, jessie, stretch and buster releases. The
transitional packages have been removed finally before the bullseye
release in August 2021.
After regular security support for buster ended in August 2022 and LTS
support ended in June 2024, I'm closing the remaining bug reports now.

Andreas