Firefox massive leaks and slows the system

[Sam_]

There're two profiles, running as independent process. One of them with usually 40 tabs open starts with mem usage of about 32-38 % and stays in this range.
Since the last update it leaks slowly over time to more then 60% and slows in fact the system. (screenshot from conky)

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: firefox 35.0.1+build1-0ubuntu0.14.04.1
ProcVersionSignature: Ubuntu 3.13.0-45.74-generic 3.13.11-ckt13
Uname: Linux 3.13.0-45-generic x86_64
AddonCompatCheckDisabled: False
ApportVersion: 2.14.1-0ubuntu3.6
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: zookeeper 2022 F.... pulseaudio
 /dev/snd/controlC0: zookeeper 2022 F.... pulseaudio
 /dev/snd/pcmC0D0p: zookeeper 2022 F...m pulseaudio
BuildID: 20150125222008
Channel: Unavailable
CurrentDesktop: Unity
Date: Tue Feb 3 21:21:13 2015
DefaultProfileIncompatibleExtensions:
 Deutsch (DE) Language Pack - <email address hidden>
 English (GB) Language Pack - <email address hidden>
 Default - {972ce4c6-7e08-4474-a285-3208198ce6fd}
DefaultProfilePrefSources:
 prefs.js
 [Profile]/extensions/{6614d11d-d21d-b211-ae23-815234e1ebb5}/defaults/preferences/preferences.js
 [Profile]/<email address hidden>/defaults/preferences/preferences.js
ForcedLayersAccel: False
IfupdownConfig:
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2012-02-05 (1094 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120204)
IpRoute:
 default via 192.168.2.1 dev eth0 proto static
 192.168.2.0/24 dev eth0 proto kernel scope link src 192.168.2.102 metric 1
IwConfig:
 eth0 no wireless extensions.

 lo no wireless extensions.
MostRecentCrashID: bp-c13399cb-b4b7-461b-8691-2a35f2141124
Profile1IncompatibleExtensions:
 Deutsch (DE) Language Pack - <email address hidden>
 English (GB) Language Pack - <email address hidden>
 Default - {972ce4c6-7e08-4474-a285-3208198ce6fd}
Profile1PrefSources:
 prefs.js
 [Profile]/<email address hidden>/defaults/preferences/preferences.js
Profiles:
 Profile0 (Default) - LastVersion=35.0.1/20150125222008 (In use)
 Profile1 - LastVersion=35.0.1/20150125222008 (In use)
RelatedPackageVersions:
 icedtea-7-plugin 1.5-1ubuntu1
 totem-mozilla 3.10.1-1ubuntu4
RfKill:

RunningIncompatibleAddons: True
SourcePackage: firefox
SubmittedCrashIDs:
 bp-c13399cb-b4b7-461b-8691-2a35f2141124
 bp-29e68126-501a-4da7-b9cd-225892140922
UpgradeStatus: Upgraded to trusty on 2014-08-12 (174 days ago)
dmi.bios.date: 07/30/2009
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 0305
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: P5QLD PRO
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: Rev X.0x
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr0305:bd07/30/2009:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnP5QLDPRO:rvrRevX.0x:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.name: System Product Name
dmi.product.version: System Version
dmi.sys.vendor: System manufacturer

[Launchpad Janitor (janitor)]

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