The documentation page you linked to now says that those key combinations are used for media seeking. It also says that tabs can be moved with Ctrl + Shift + Page Up and Ctrl + Shift + Page Down. I've tested this on Firefox 53.0.2 on Ubuntu 17.04 "Zesty Zapus" and can confirm it works.
** Changed in: firefox (Ubuntu) Status: Confirmed => Fix Released -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to firefox in Ubuntu. https://bugs.launchpad.net/bugs/997640 Title: Keyboard shortcuts for moving tabs don't work Status in firefox package in Ubuntu: Fix Released Bug description: Per http://support.mozilla.org/en-US/kb/Keyboard%20shortcuts #w_windows-tabs I should be able to move tabs around by using Ctrl + → or Ctrl + ←, but neither works. I can move tabs around in Chrome using Ctrl + Shift + PgUp/PgDown. ProblemType: Bug DistroRelease: Ubuntu 12.04 Package: firefox 12.0+build1-0ubuntu0.12.04.1 ProcVersionSignature: Ubuntu 3.2.0-24.37-generic-pae 3.2.14 Uname: Linux 3.2.0-24-generic-pae i686 AddonCompatCheckDisabled: False AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24. ApportVersion: 2.0.1-0ubuntu7 Architecture: i386 ArecordDevices: **** List of CAPTURE Hardware Devices **** card 0: PCH [HDA Intel PCH], device 0: CONEXANT Analog [CONEXANT Analog] Subdevices: 1/1 Subdevice #0: subdevice #0 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC0: mthaddon 1939 F.... pulseaudio /dev/snd/pcmC0D0p: mthaddon 1939 F...m pulseaudio BuildID: 20120423122624 Card0.Amixer.info: Card hw:0 'PCH'/'HDA Intel PCH at 0xf2520000 irq 45' Mixer name : 'Intel CougarPoint HDMI' Components : 'HDA:14f1506e,17aa21da,00100002 HDA:80862805,80860101,00100000' Controls : 26 Simple ctrls : 8 Card29.Amixer.info: Card hw:29 'ThinkPadEC'/'ThinkPad Console Audio Control at EC reg 0x30, fw unknown' Mixer name : 'ThinkPad EC (unknown)' Components : '' Controls : 1 Simple ctrls : 1 Card29.Amixer.values: Simple mixer control 'Console',0 Capabilities: pswitch pswitch-joined penum Playback channels: Mono Mono: Playback [on] Channel: release CheckboxSubmission: e9bd5d0c11367f73e7718b1ea675f7ba CheckboxSystem: bb422ca46d02494cdbc459927a98bc2f Date: Thu May 10 14:44:01 2012 ForcedLayersAccel: False IfupdownConfig: auto lo iface lo inet loopback InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Beta i386 (20110921.2) IpRoute: default via 10.45.43.1 dev wlan0 proto static 10.0.3.0/24 dev lxcbr0 proto kernel scope link src 10.0.3.1 10.45.43.0/24 dev wlan0 proto kernel scope link src 10.45.43.120 metric 2 169.254.0.0/16 dev wlan0 scope link metric 1000 192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 Profiles: Profile0 (Default) - LastVersion=12.0/20120423122624 (Running) RunningIncompatibleAddons: False SourcePackage: firefox UpgradeStatus: Upgraded to precise on 2012-02-02 (98 days ago) dmi.bios.date: 07/07/2011 dmi.bios.vendor: LENOVO dmi.bios.version: 8DET50WW (1.20 ) dmi.board.asset.tag: Not Available dmi.board.name: 4287CTO dmi.board.vendor: LENOVO dmi.board.version: Not Available dmi.chassis.asset.tag: No Asset Information dmi.chassis.type: 10 dmi.chassis.vendor: LENOVO dmi.chassis.version: Not Available dmi.modalias: dmi:bvnLENOVO:bvr8DET50WW(1.20):bd07/07/2011:svnLENOVO:pn4287CTO:pvrThinkPadX220:rvnLENOVO:rn4287CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable: dmi.product.name: 4287CTO dmi.product.version: ThinkPad X220 dmi.sys.vendor: LENOVO To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/997640/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp