Firefox use 100% of one CPU (Mac)

Question

I use last firefox (32) on MacOS X 10.6.8.
Sometime firefox start using 100% a one CPU, from that time the only way to stop it was to quit (it take severals seconds, sometime it hang). When it start i can close all windows, firefox continue using 100% CPU.
I follow standard instructions (update to lastest, disable plugins and extensions...) it do not work.
I not a configuration to reproduce the problem : keep iCloud mail open in one tab is the way to reproduce the problem sometime after a few minutes, sometime after some hours : but it also happend sometime with no iCloud open...
Paramètres de base de l'application
Nom: Firefox
Version: 32.0.3
Agent utilisateur: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:32.0) Gecko/20100101 Firefox/32.0
Rapports de plantage des 3 derniers jours
Tous les rapports de plantage
Extensions
Nom: Firebug
Version: 2.0.4
Activée: true
ID: [email protected]
Nom: Adblock Plus
Version: 2.6.5
Activée: false
ID: {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}
Nom: Copy Plain Text 2
Version: 1.3.2
Activée: false
ID: [email protected]
Nom: DuckDuckGo Plus
Version: 0.4.2
Activée: false
ID: jid1-ZAdIEUB7XOzOJw@jetpack
Nom: Lightbeam
Version: 1.0.10.2
Activée: false
ID: jid1-F9UJ2thwoAm5gQ@jetpack
Nom: Readability
Version: 2.4
Activée: false
ID: {6005d9b1-d115-485a-a92a-3f6453ca3fe2}
Accélération graphique
Fenêtres avec accélération graphique: 1/1 OpenGL (OMTC)
ID du périphérique: 0x9583
ID du vendeur: 0x1002
Rendu WebGL: ATI Technologies Inc. -- ATI Radeon HD 2600 PRO OpenGL Engine
windowLayerManagerRemote: true
AzureCanvasBackend: quartz
AzureContentBackend: quartz
AzureFallbackCanvasBackend: none
AzureSkiaAccelerated: 0
Préférences modifiées importantes
accessibility.typeaheadfind.flashBar: 0
browser.cache.disk.capacity: 358400
browser.cache.disk.smart_size_cached_value: 358400
browser.cache.disk.smart_size.first_run: false
browser.cache.disk.smart_size.use_old_max: false
browser.cache.frecency_experiment: 3
browser.history_expire_days.mirror: 180
browser.places.importBookmarksHTML: false
browser.places.smartBookmarksVersion: 7
browser.search.useDBForOrder: true
browser.sessionstore.upgradeBackup.latestBuildID: 20140923175406
browser.startup.homepage: about:newtab|http://www.charentelibre.fr/charente/pays-de-cognac/|http://www.sudouest.fr/charente/cognac/|https://www.ic
browser.startup.homepage_override.buildID: 20140923175406
browser.startup.homepage_override.mstone: 32.0.3
dom.mozApps.used: true
dom.w3c_touch_events.expose: false
extensions.lastAppVersion: 32.0.3
font.internaluseonly.changed: false
font.size.fixed.x-western: 12
font.size.variable.x-western: 14
gfx.blacklist.direct2d: 3
gfx.blacklist.layers.direct3d9: 3
gfx.blacklist.webgl.msaa: 4
network.cookie.prefsMigrated: true
places.database.lastMaintenance: 1414486056
places.history.expiration.transient_current_max_pages: 104858
places.last_vacuum: 1341938581
plugin.disable_full_page_plugin_for_types: application/pdf
plugin.importedState: true
plugin.state.adobepdfviewernpapi: 0
plugin.state.divxbrowserplugin: 0
plugin.state.flash: 1
plugin.state.flip4mac wmv plugin: 0
plugin.state.google earth web plug-in: 1
plugin.state.iphotophotocast: 1
plugin.state.silverlight: 0
print.macosx.pagesetup-2: PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPCFET0NUWVBFIHBsaXN0IFBVQkxJQyAiLS8vQXBwbGUvL0RURCBQTElTVCAxLjAvL0VO
print.print_bgcolor: false
print.print_bgimages: false
print.print_colorspace:
print.print_command:
print.print_downloadfonts: true
print.print_duplex: 0
print.print_evenpages: true
print.print_in_color: true
print.print_margin_bottom: 0.5
print.print_margin_left: 0.5
print.print_margin_right: 0.5
print.print_margin_top: 0.5
print.print_oddpages: true
print.print_orientation: 0
print.print_page_delay: 50
print.print_pagedelay: 500
print.print_paper_data: 0
print.print_paper_height: 11.00
print.print_paper_name:
print.print_paper_size: 0
print.print_paper_size_type: 1
print.print_paper_size_unit: 0
print.print_paper_width: 8.50
print.print_plex_name:
print.print_printer:
print.print_resolution: 0
print.print_resolution_name:
print.print_reversed: false
print.print_scaling: 1.00
print.print_shrink_to_fit: true
print.print_to_file: false
print.print_unwriteable_margin_bottom: 17
print.print_unwriteable_margin_left: 19
print.print_unwriteable_margin_right: 18
print.print_unwriteable_margin_top: 17
privacy.donottrackheader.enabled: true
privacy.sanitize.migrateFx3Prefs: true
security.warn_viewing_mixed: false
storage.vacuum.last.index: 1
storage.vacuum.last.places.sqlite: 1413879484
JavaScript
Ramasse-miettes incrémentiel: true
Accessibilité
Activée: false
Empêcher l'accessibilité: 0
Versions des bibliothèques
NSPR
Version minimale attendue: 4.10.6
Version utilisée: 4.10.6
NSS
Version minimale attendue: 3.16.5 Basic ECC
Version utilisée: 3.16.5 Basic ECC
NSSSMIME
Version minimale attendue: 3.16.5 Basic ECC
Version utilisée: 3.16.5 Basic ECC
NSSSSL
Version minimale attendue: 3.16.5 Basic ECC
Version utilisée: 3.16.5 Basic ECC
NSSUTIL
Version minimale attendue: 3.16.5
Version utilisée: 3.16.5
Fonctionnalités expérimentales
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Answer 1

It doesn't help, has i said : i allready do standard procédure to help (what you point) : update to lastest, disable extension or theme (i do not use), disable plug-ins... nothing helps, the bug is still there.