Since earlier today I have found that after about 10 minutes or less of using Firefox that suddenly for no apparent reason pages will refuse to load any contents, and although Firefox does not take me to the page which says it can't reach the site, it doesn't manage to load anything as though its internet connection has suddenly been lost. It won't even let me check for updates for plugins and gives an error for that. I have tested with other applications such as ping and the internet connection is fine, it's just Firefox which loses it.

I have noticed that when I run firefox from Terminal that this is the output to begin with:

    1482487989643 <email address hidden> WARN Loading extension '<email address hidden>': Reading manifest: Error processing background.persistent: Event pages are not currently supported. This will run as a persistent background page.
    1482487989666 <email address hidden> WARN Loading extension '<email address hidden>': Reading manifest: Error processing author: An unexpected property was found in the WebExtension manifest.
    1482487989666 <email address hidden> WARN Loading extension '<email address hidden>': Reading manifest: Error processing version_name: An unexpected property was found in the WebExtension manifest.
    1482487989666 <email address hidden> WARN Loading extension '<email address hidden>': Reading manifest: Error processing options_page: An unexpected property was found in the WebExtension manifest.
    1482487989708 <email address hidden> WARN Please specify whether you want browser_style or not in your browser_action options.
    Promise resolved after context unloaded

Then when the problem starts to occur, I find that the only way to resolve it, if even for a short period, is to restart the browser, so I tell Firefox to quit, however although the window does close, the process carries on and this is the output:

    tabs.onRemoved event fired after context unloaded.
    tabs.onRemoved event fired after context unloaded.
    tabs.onRemoved event fired after context unloaded.
    console.error:
      Message: Error: SessionFile is closed
      Stack:
        SessionFileInternal.write@resource://app/modules/sessionstore/SessionFile.jsm:315:29
    this.SessionFile.write@resource://app/modules/sessionstore/SessionFile.jsm:76:12
    SessionSaverInternal._writeState@resource://app/modules/sessionstore/SessionSaver.jsm:259:12
    SessionSaverInternal._saveState@resource://app/modules/sessionstore/SessionSaver.jsm:230:12
    SessionSaverInternal._saveStateAsync@resource://app/modules/sessionstore/SessionSaver.jsm:243:5
    SessionSaverInternal.runDelayed/this._timeoutID<@resource://app/modules/sessionstore/SessionSaver.jsm:147:40
    setTimeout_timer@resource://gre/modules/Timer.jsm:30:5

    ExceptionHandler::GenerateDump cloned child 12324
    ExceptionHandler::SendContinueSignalToChild sent continue signal to child
    ExceptionHandler::WaitForContinueSignal waiting for continue signal...

I am then told that Firefox crashed and asked if I would like to submit a report, so far I have told it to submit a report three times as the crash has occurred that number of times.

For that entire period of time this is the output from Firefox in syslog:

    Dec 23 10:00:42 <computer-name> firefox.desktop[11349]: 1482487242751#<email address hidden>#011WARN#011Loading extension '<email address hidden>': Reading manifest: Error processing background.persistent: Event pages are not currently supported. This will run as a persistent background page.
    Dec 23 10:00:42 <computer-name> firefox.desktop[11349]: 1482487242778#<email address hidden>#011WARN#011Loading extension '<email address hidden>': Reading manifest: Error processing author: An unexpected property was found in the WebExtension manifest.
    Dec 23 10:00:42 <computer-name> firefox.desktop[11349]: 1482487242779#<email address hidden>#011WARN#011Loading extension '<email address hidden>': Reading manifest: Error processing version_name: An unexpected property was found in the WebExtension manifest.
    Dec 23 10:00:42 <computer-name> firefox.desktop[11349]: 1482487242779#<email address hidden>#011WARN#011Loading extension '<email address hidden>': Reading manifest: Error processing options_page: An unexpected property was found in the WebExtension manifest.
    Dec 23 10:00:42 <computer-name> firefox.desktop[11349]: 1482487242821#<email address hidden>#011WARN#011Please specify whether you want browser_style or not in your browser_action options.
    Dec 23 10:01:00 <computer-name> firefox.desktop[11349]: Promise resolved after context unloaded
    Dec 23 10:10:37 <computer-name> firefox.desktop[11349]: Promise resolved after context unloaded
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: console.error:
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: Message: [Exception... "Component returned failure code: 0x80520006 (NS_ERROR_FILE_TARGET_DOES_NOT_EXIST) [nsIFile.directoryEntries]" nsresult: "0x80520006 (NS_ERROR_FILE_TARGET_DOES_NOT_EXIST)" location: "JS frame :: resource://gre/modules/commonjs/toolkit/loader.js -> resource://jid1-oonoa6xbjznvlq-at-jetpack/lib/main.js :: deleteTempFiles :: line 252" data: no]
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: Stack:
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: deleteTempFiles@resource://gre/modules/commonjs/toolkit/loader.js -> resource://jid1-oonoa6xbjznvlq-at-jetpack/lib/main.js:252:7
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: exports.onUnload@resource://gre/modules/commonjs/toolkit/loader.js -> resource://jid1-oonoa6xbjznvlq-at-jetpack/lib/main.js:322:3
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: unload/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/system/unload.js:79:9
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: unload@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/system/unload.js:73:3
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: onunload@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/system/unload.js:99:5
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: Observer<.observe@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/system/events.js:81:7
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: unload@resource://gre/modules/commonjs/toolkit/loader.js:954:3
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: unload/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/addon/bootstrap.js:153:9
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: unload@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/addon/bootstrap.js:149:12
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: shutdown@resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/commonjs/sdk/addon/bootstrap.js:146:12
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: this.XPIProvider.callBootstrapMethod@resource://gre/modules/addons/XPIProvider.jsm:4800:9
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: this.XPIProvider.startup/<.observe@resource://gre/modules/addons/XPIProvider.jsm:2811:15
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: tabs.onRemoved event fired after context unloaded.
    Dec 23 10:11:25 <computer-name> firefox.desktop[11349]: message repeated 2 times: [ tabs.onRemoved event fired after context unloaded.]
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: console.error:
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: Message: Error: SessionFile is closed
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: Stack:
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: SessionFileInternal.write@resource://app/modules/sessionstore/SessionFile.jsm:315:29
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: this.SessionFile.write@resource://app/modules/sessionstore/SessionFile.jsm:76:12
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: SessionSaverInternal._writeState@resource://app/modules/sessionstore/SessionSaver.jsm:259:12
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: SessionSaverInternal._saveState@resource://app/modules/sessionstore/SessionSaver.jsm:230:12
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: SessionSaverInternal._saveStateAsync@resource://app/modules/sessionstore/SessionSaver.jsm:243:5
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: SessionSaverInternal.runDelayed/this._timeoutID<@resource://app/modules/sessionstore/SessionSaver.jsm:147:40
    Dec 23 10:11:40 <computer-name> firefox.desktop[11349]: setTimeout_timer@resource://gre/modules/Timer.jsm:30:5
    Dec 23 10:12:29 <computer-name> firefox.desktop[11349]: ExceptionHandler::GenerateDump cloned child 11985
    Dec 23 10:12:29 <computer-name> firefox.desktop[11349]: ExceptionHandler::SendContinueSignalToChild sent continue signal to child
    Dec 23 10:12:29 <computer-name> firefox.desktop[11349]: ExceptionHandler::WaitForContinueSignal waiting for continue signal...

I am running Ubuntu GNOME 16.10 with GNOME 3.22 and Firefox 50. Although I am sad to say this, if I don't find a solution for this issue soon I am at least temporarily going to have to switch browsers because Firefox is seriously becoming unusable with this issue.

Firefox troubleshooting information:

Application Basics
------------------

Name: Firefox
Version: 50.1.0
Build ID: 20161209093710
User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0
OS: Linux 4.8.0-32-generic
Multiprocess Windows: 0/1 (Disabled by add-ons)
Safe Mode: false

Crash Reports for the Last 3 Days
---------------------------------

Report ID: bp-5e9c4d15-befb-4179-bae3-188c02161223
Submitted: 20 minutes ago

Report ID: bp-c43e457e-4eaf-4e6b-bf2c-58a4d2161223
Submitted: 38 minutes ago

Report ID: bp-499fd361-4452-4ced-bcb8-5cb712161223
Submitted: 50 minutes ago

Report ID: bp-c5dd97f9-d864-49c9-b523-f32d92161223
Submitted: 1 hour ago

All Crash Reports

Extensions
----------

Name: Adblock Plus
Version: 2.8.2
Enabled: true
ID: {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}

Name: Application Update Service Helper
Version: 1.0
Enabled: true
ID: <email address hidden>

Name: Download YouTube Videos as MP4
Version: 1.8.8
Enabled: true
ID: {b9bfaf1c-a63f-47cd-8b9a-29526ced9060}

Name: Ghostery
Version: 7.1.1.5
Enabled: true
ID: <email address hidden>

Name: GNotifier
Version: 1.9.8
Enabled: true
ID: jid1-OoNOA6XBjznvLQ@jetpack

Name: HTTPS Everywhere
Version: 5.2.9
Enabled: true
ID: <email address hidden>

Name: Multi-process staged rollout
Version: 1.5
Enabled: true
ID: <email address hidden>

Name: NoScript
Version: 2.9.5.2
Enabled: true
ID: {73a6fe31-595d-460b-a920-fcc0f8843232}

Name: Pocket
Version: 1.0.5
Enabled: true
ID: <email address hidden>

Name: TrafficLight
Version: 0.2.23.1-signed.1-signed
Enabled: true
ID: <email address hidden>

Name: uBlock Origin
Version: 1.10.4
Enabled: true
ID: <email address hidden>

Name: Ubuntu Modifications
Version: 3.2
Enabled: true
ID: <email address hidden>

Name: uMatrix
Version: 0.9.3.6
Enabled: true
ID: <email address hidden>

Name: VTzilla
Version: 1.5.1-signed.1-signed
Enabled: true
ID: <email address hidden>

Name: Web Compat
Version: 1.0
Enabled: true
ID: <email address hidden>

Name: Mailvelope
Version: 1.6.0
Enabled: false
ID: jid1-AQqSMBYb0a8ADg@jetpack

Graphics
--------

Features
Compositing: Basic
Asynchronous Pan/Zoom: none
WebGL Renderer: Intel Open Source Technology Center -- Mesa DRI Intel(R) Sandybridge Mobile
WebGL2 Renderer: (no info)
Hardware H264 Decoding: No
Audio Backend: pulse
GPU #1
Active: Yes
Description: Intel Open Source Technology Center -- Mesa DRI Intel(R) Sandybridge Mobile
Vendor ID: Intel Open Source Technology Center
Device ID: Mesa DRI Intel(R) Sandybridge Mobile
Driver Version: 3.0 Mesa 12.0.3

Diagnostics
AzureCanvasAccelerated: 0
AzureCanvasBackend: skia
AzureContentBackend: cairo
AzureFallbackCanvasBackend: none
CairoUseXRender: 0
Decision Log
HW_COMPOSITING:
blocked by default: Acceleration blocked by platform
OPENGL_COMPOSITING:
unavailable by default: Hardware compositing is disabled

Important Modified Preferences
------------------------------

accessibility.blockautorefresh: true
accessibility.typeaheadfind.flashBar: 0
browser.cache.disk.capacity: 0
browser.cache.disk.enable: false
browser.cache.disk.filesystem_reported: 1
browser.cache.disk.smart_size.enabled: false
browser.cache.disk.smart_size.first_run: false
browser.cache.disk.smart_size.use_old_max: false
browser.cache.frecency_experiment: 3
browser.download.importedFromSqlite: true
browser.download.manager.showAlertOnComplete: false
browser.places.smartBookmarksVersion: 8
browser.search.useDBForOrder: true
browser.sessionstore.upgradeBackup.latestBuildID: 20161209093710
browser.startup.homepage: https://mail.google.com/mail/u/0/#inbox|https://askubuntu.com/questions|https://chat.stackexchange.com/?tab=favorite&sor
browser.startup.homepage_override.buildID: 20161209093710
browser.startup.homepage_override.mstone: 50.1.0
browser.tabs.remote.autostart.2: true
browser.urlbar.userMadeSearchSuggestionsChoice: true
dom.apps.lastUpdate.buildID: 20161025164528
dom.apps.lastUpdate.mstone: 49.0.2
dom.apps.reset-permissions: true
dom.max_chrome_script_run_time: 40
dom.max_script_run_time: 40
dom.mozApps.used: true
extensions.lastAppVersion: 50.1.0
font.internaluseonly.changed: false
media.eme.enabled: true
media.gmp-gmpopenh264.abi: x86_64-gcc3
media.gmp-gmpopenh264.lastUpdate: 1474759853
media.gmp-gmpopenh264.version: 1.6
media.gmp-manager.buildID: 20161209093710
media.gmp-manager.lastCheck: 1482484692
media.gmp-widevinecdm.abi: x86_64-gcc3
media.gmp-widevinecdm.lastUpdate: 1480275530
media.gmp-widevinecdm.version: 1.4.8.903
media.gmp.storage.version.observed: 1
media.peerconnection.ice.default_address_only: true
network.cookie.cookieBehavior: 1
network.cookie.prefsMigrated: true
network.dns.disablePrefetch: true
network.http.referer.XOriginPolicy: 1
network.http.speculative-parallel-limit: 0
network.predictor.cleaned-up: true
network.prefetch-next: false
places.database.lastMaintenance: 1482000635
places.history.expiration.transient_current_max_pages: 61201
plugin.disable_full_page_plugin_for_types: application/pdf
plugin.importedState: true
plugin.state.flash: 0
plugin.state.libgnome-shell-browser-plugin: 2
privacy.clearOnShutdown.cookies: false
privacy.clearOnShutdown.downloads: false
privacy.clearOnShutdown.formdata: false
privacy.clearOnShutdown.history: false
privacy.donottrackheader.enabled: true
privacy.sanitize.migrateClearSavedPwdsOnExit: true
privacy.sanitize.sanitizeOnShutdown: true
security.ssl.errorReporting.automatic: true
services.sync.declinedEngines:
storage.vacuum.last.index: 1
storage.vacuum.last.places.sqlite: 1481839361

Important Locked Preferences
----------------------------

Places Database
---------------

JavaScript
----------

Incremental GC: true

Accessibility
-------------

Activated: false
Prevent Accessibility: 0

Library Versions
----------------

NSPR
Expected minimum version: 4.12
Version in use: 4.12

NSS
Expected minimum version: 3.26.2
Version in use: 3.26.2

NSSSMIME
Expected minimum version: 3.26.2
Version in use: 3.26.2

NSSSSL
Expected minimum version: 3.26.2
Version in use: 3.26.2

NSSUTIL
Expected minimum version: 3.26.2
Version in use: 3.26.2

Experimental Features
---------------------

Sandbox
-------

Seccomp-BPF (System Call Filtering): true
Seccomp Thread Synchronisation: true
User Namespaces: true
Media Plugin Sandboxing: true

I originally reported this issue here: https://bugs.launchpad.net/ubuntu-gnome/+bug/1652272 But thought I should also do so upstream. Some extra information about Firefox and the system are available from Apport at the downstream bug report.