Right hand scroll bar causes screen to go black

[Earl Ruby]

Binary package hint: firefox

Firefox 3.6.13
Ubuntu 10.10 / Gnome

This problem has actually been plaguing me for a while, through previous versions of Ubuntu and Firefox, but it took me a while to figure out how to reliably reproduce the problem and trace it back to Firefox.

I use two Viewsonic 22" 1680x1050 monitors on my Ubuntu box that are attached using an ATI Technologies RV516 [Radeon X1300/X1550 Series] video card with 2 DVI ports. I use Ubuntu's System > Preferences > Monitors to set the monitors in a side by side (left/right) configuration.

If I maximize Firefox on the right hand screen and pull up a tab with enough content to display a right-hand scroll bar, when I scroll to the bottom of the window the entire right hand screen goes black. If I use the mouse wheel to scroll up the right hand screen comes back to life. Scroll down, screen goes black, scroll up, screen comes back.

I have tried repeating this with other browsers and other programs that have scroll bars. The error only happens with Firefox, and only if Firefox is maximized on the right-hand screen. If Firefox is not maximized or if I have Firefox maximized on the left hand screen I cannot reproduce the problem.

I have tried swapping video cables and swapping monitors to make sure that this is not a hardware problem but the problem always happens on the right hand screen regardless of what hardware I'm using.

It does not happen with every HTML page that scrolls, but it happens often, and when it does happen I can reproduce the problem again and again.

I suspect that there's a math or rounding error somewhere in the scroll bar code that for certain HTML page sizes, when the page size is divided into the available window area, you end up with a rounding error that manifests itself when the scroll bar handle reaches the bottom of the page. At that point Firefox attempts to display the scroll bar handle below the end of the scroll bar, and that causes the window manager to blank the screen. I suspect that the error is ignored by most window managers and if it wasn't for the fact that I'm using a two-screen setup I probably wouldn't see it either.

Could someone familiar with the code that calculates the scrolling of windows check the code and verify that the math is correct for when a scroll bar handle is pulled to the bottom of the screen in all cases?

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: firefox 3.6.13+build3+nobinonly-0ubuntu0.10.10.1
ProcVersionSignature: Ubuntu 2.6.35-24.42-server 2.6.35.8
Uname: Linux 2.6.35-24-server x86_64
Architecture: amd64
Date: Thu Jan 6 10:46:40 2011
FirefoxPackages:
 firefox 3.6.13+build3+nobinonly-0ubuntu0.10.10.1
 firefox-gnome-support 3.6.13+build3+nobinonly-0ubuntu0.10.10.1
 firefox-branding 3.6.13+build3+nobinonly-0ubuntu0.10.10.1
 abroswer N/A
 abrowser-branding N/A
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.utf8
 SHELL=/bin/bash
SourcePackage: firefox

[Ramon Grullon (rgrullon)]

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