Page up/dn keys stop working on a page

[Steve Magoun]

Occasionally Firefox stops responding to my keyboard's page up/down keys. When this happens, it only affects a single page. Page up/down will keep working in other tabs. Reloading the page or navigating to a new page is enough to clear the problem. I can reproduce this most frequently with launchpad bug pages. When this happens, the scroll bars continue to function and so does the scroll wheel on my mouse; it's just the page up/dn keys that stop working. It's not a focus problem; clicking inside the browser window to ensure it has focus does not help.

To reproduce:
1) Open a few browser tabs
2) In one tab, load a launchpad bug page like https://bugs.launchpad.net/ubuntu/+source/linux-lts-quantal/+bug/1088454
3) Use page up/down on your keyboard to scroll the page up/down

Expected results:
The page up/down keys scroll the page up/down

Actual results:
The page up/down keys have no discernable effect on the affected browser tab

If I had to guess I'd say this happens on about 0.1-0.5% of the web pages I load, which is enough to see it a few times a week.

I observed the problem in FF 18 on 12.10. It happens in FF 19 on 13.04 too

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: firefox 19.0~b2+build1-0ubuntu1
ProcVersionSignature: Ubuntu 3.8.0-1.5-generic 3.8.0-rc4
Uname: Linux 3.8.0-1-generic x86_64
NonfreeKernelModules: nvidia
AddonCompatCheckDisabled: False
ApportVersion: 2.8-0ubuntu2
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: steve 2350 F.... pulseaudio
 /dev/snd/pcmC0D0p: steve 2350 F...m pulseaudio
BuildID: 20130117090125
Channel: Unavailable
Date: Mon Jan 28 14:47:57 2013
ForcedLayersAccel: False
IfupdownConfig:
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2010-09-17 (864 days ago)
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Beta amd64 (20100901.1)
IpRoute:
 default via 10.0.1.1 dev wlan0 proto static
 10.0.1.0/24 dev wlan0 proto kernel scope link src 10.0.1.121 metric 9
 169.254.0.0/16 dev wlan0 scope link metric 1000
MarkForUpload: True
MostRecentCrashID: bp-f68bddea-16ef-4f42-bc63-916352121120
Plugins:
 iTunes Application Detector - /usr/lib/mozilla/plugins/librhythmbox-itms-detection-plugin.so (rhythmbox-mozilla)
 Google Talk Plugin Video Accelerator - /opt/google/talkplugin/libnpgtpo3dautoplugin.so (google-talkplugin)
 Google Talk Plugin - /opt/google/talkplugin/libnpgoogletalk.so (google-talkplugin)
 Shockwave Flash - /usr/lib/mozilla/plugins/libflashplayer.so
 HP Virtual Rooms Plug-in - [HomeDir]/.mozilla/plugins/hpvirtualrooms-plugin.so
PrefSources: prefs.js
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
Profiles: Profile0 (Default) - LastVersion=19.0/20130117090125 (In use)
RelatedPackageVersions:
 rhythmbox-mozilla 2.98-0ubuntu3
 google-talkplugin 3.10.2.0-1
RfKill:
 1: phy1: Wireless LAN
  Soft blocked: no
  Hard blocked: no
RunningIncompatibleAddons: False
SourcePackage: firefox
UpgradeStatus: Upgraded to raring on 2013-01-25 (3 days ago)
dmi.bios.date: 03/05/08
dmi.bios.vendor: Apple Inc.
dmi.bios.version: MBP31.88Z.0070.B07.0803051658
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: Mac-F4238BC8
dmi.board.vendor: Apple Inc.
dmi.board.version: PVT
dmi.chassis.asset.tag: Asset Tag#
dmi.chassis.type: 2
dmi.chassis.vendor: Apple Inc.
dmi.chassis.version: Mac-F4238BC8
dmi.modalias: dmi:bvnAppleInc.:bvrMBP31.88Z.0070.B07.0803051658:bd03/05/08:svnAppleInc.:pnMacBookPro3,1:pvr1.0:rvnAppleInc.:rnMac-F4238BC8:rvrPVT:cvnAppleInc.:ct2:cvrMac-F4238BC8:
dmi.product.name: MacBookPro3,1
dmi.product.version: 1.0
dmi.sys.vendor: Apple Inc.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.