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Firefox ESR large text file rendering problem

I have stumbled on a rendering problem with Firefox-45-ESR and
Firefox-52-ESR on Debian-8-stable (jessie) and Debian-7-LTS (wheezy).
Firefox is unable to render long text files correctly. At least not with
default settings. This happens on Debian stable and LTS precompiled versions
of Firefox-45-ESR, and also self compiled versions on Firefox-45-ESR and
Firefox-52-ESR, also with newer gcc versions. My test computer is running
old-school sysV-init and fvwm window manager. The problem occours on both
bare-metal hardware (intel graphics driver) and Qemu virtual machine
(-vga std) so graphics driver does not appear the be the problem.

I also booted Ubuntu-16.04.2 live-DVD image. This problem does not occour on
that live-DVD, so this appears to be Debian specific.

Example long text file, 33+ megabytes:


Same rendering problem happens if that is loaded from local


Demo screenshot, beginning of the page, this is OK:


Demo screenshot, end of the page, this is rendered incorrectly:


The beginning of the page is rendered correctly, but end of the page is not.
To see the "mess" press the END key on the keyboard, or scroll the page to
the end. Then maybe press cursor-UP and cursor-DOWN keys to scroll the page,
more "mess" appears.

On Firefox-45-ESR (and older versions) this bug can be worked around by
setting these in about:config

 html5.offmainthread = false
 layers.offmainthreadcomposition.async-animations = false
 layers.offmainthreadcomposition.enabled = false

The problem is that Firefox-52-ESR is soon the be the only security
maintained version, and that version no longer respects those
"offmainthread" workarounds.

Any ideas how to work around this problem on Firefox-52-ESR?

Jari Ruusu  4096R/8132F189 12D6 4C3A DCDA 0AA4 27BD  ACDF F073 3C80 8132 F189

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