Mozilla products by default send some information to NSA. This guide will show you how to change these settings to other secret service of your choice or how to turn them off completely.

See also list of other applications that do not respect privacy.

Check Advanced → Certificates → Ask me every time, we really don't want to authenticate to the remote server automatically! Exploited in the wild!

This applies to Firefox <57. We have downloaded Firefox 57, started it, left it for ~30 minutes and were amazed:

• Run with parameter -P. Select “Start offline”. Please note that Firefox at least since version 67 ignore offline parameter for captive portal requests anyway, and perform HTTP requests against detectportal.firefox.com.
• Visit Preferences. In “Security”, turn off “Block reported attack sites” and “Block reported web forgeries”
• Uncheck Advanced → Updates
• Uncheck Advanced → Certificates → Validation → OCSP (of course this disables fetching certificate revocation info - be sure you know what are you doing)
• Visit about:config. Set extensions.blocklist.enabled = false.
• Search for “http”. Change all URLs to nsalitomerice.cz, localhost or other secret service of your choice.
• Unfortunately, Firefox will still download favicons from Google, Yahoo and Mibbit (incl. cookies) when browsing Preferences in a certain way. Bugreport pending.
  • Related: about:addons loads Google Analytics
• Since FF 32, on Windows, hashes of certain downloaded files are sent to Google. This can be disabled by the aforementioned settings. 1, 2
• If you want to test this with an intercepting proxy, make sure you have security.cert_pinning.enforcement_level 0 or 1
• Disable automatic resolving of local names and URL-like patters: set browser.fixup.alternate.enabled and keyword.enabled to false. PT
• media.peerconnection.enabled: false (enumhosts, mirror)

• Since version 33, some plugins seem to be downloaded automatically. Set media.gmp-gmpopenh264.autoupdate = false.
  • Since version 38, it is not possible to turn this feature off. Additionally, the downloaded binary contained a buffer overflow.
    • media.gmp-gmpopenh264.enabled does not help and media.gmp-gmpopenh264.autoupdate does note exist anymore. Try setting media.gmp-manager.lastCheck to the future and media.gmp-manager.url to some non-existent URL.
• Since version 38 (on Windows), a DRM backdoor from Adobe is downloaded automatically: The CDM will be downloaded from Adobe shortly after you upgrade or install Firefox and will be activated when you first interact with a site that uses Adobe CDM.
  • This will be fixed in version 52.
  • However, in version 57, another DRM backdoor is downloaded on all platforms. How to disable.

• Every time you open new window, Firefox posts your system information to Mozilla, e.g. this one. This can be avoided by aforementioned URL settings or by setting homepage to about:blank.

• network.dns.disablePrefetch, network.prefetch-next: false

• Yes, we have API for manipulating browser history. I have no idea if something interesting can be done with it. See browser.history.allow* in about:config.
  • Setting this to False breaks webpages, known problems are with zbozi.cz and mapy.cz.

• devtools.gcli.jquerySrc = https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js
• devtools.gcli.lodashSrc = https://cdnjs.cloudflare.com/ajax/libs/lodash.js/2.4.1/lodash.min.js
• devtools.gcli.underscoreSrc = https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.7.0/underscore-min.js

• Files in local filesystem can read files in current directory and post them to a remote server.
  • Download this image to your home directory and open it in Firefox.

• Trusting CAs caught forging certificates

• HSTS settings cannot be overriden (the decision can be hand-deleted from SiteSecurityServiceState.txt when Firefox is not running (otherwise the file is immediately overwritten), however, if the page sends further broken HSTS headers, subsequent requests will fail anyway). This is in compliance with RFC 6797, section 12.1. NSA Litoměřice believes that this is one of RFCs that are badly designed and should be ignored (the other being e.g. RFC 826, which we describe here)
  • You can override it by adding test.currentTimeOffsetSeconds (integer) = 11491200
  • And in Chrome, you can override it by typing “badidea” on the error page
    • or “thisisunsafe” in newer (2018-03) versions of Chrome
  • Neither it seems to be possible to override revoked certificate
• The webpage can detect that element inspector is opened. This should be possible to disable too…

• Recommended: network.IDN_show_punycode = true (more info)

• Firefox 52 ESR downloads browser.safebrowsing.provider.mozilla.gethashURL even if safe browsing is turned off in Preferences

• Some webpages are blocking pasting of password for “better security”, so you cannot use a password manager. Set dom.event.clipboardevents.enabled=false to disable this. This may also mitigate some attacks with clipboard leaking, or replacing content of clipboard with a malicious command

See: Firefox hardening

See also this guide. I have downloaded it from an onion service and put it here for those who don't have access to the darknet.

To be investigated:

• https://blog.lukaszolejnik.com/stealing-sensitive-browser-data-with-the-w3c-ambient-light-sensor-api/
• https://www.ghacks.net/2017/07/13/privacy-blunder-firefox-getaddons-page-google-analytics/

After these changes, firefox should not open any outgoing connections (if autoupdate was disabled by company policy / Linux distribution maintainers) when starting with a blank page, except for checking updates of installed extensions.

XXX TODO: How to get rid of:

1. POST https://shavar.services.mozilla.com/downloads?client=navclient-auto-ffox&appver=...&pver=2.2
2. GET https://firefox.settings.services.mozilla.com/v1/buckets/pinning/collections/pins?_expected=148…..

(once a day? with a bunch of similar requests)

1. GET https://content-signature-2.cdn.mozilla.net/chains/remote-settings.content-signature.mozilla.org-2020-07-06-00-19-31.chain

• General
  • Firefox Updates
    • Automatically update search engines → Off
  • Browsing
    • Search for text when you start typing → Off
    • Recommend extensions as you browse → Off
• Privacy & security
  • Browser Privacy
    • Block trackers → Always
    • Send DNT → Always
  • Firefox Data Collection and Use
    • Allow Firefox to install and run studies → Off
    • Allow Firefox to send technical and interaction data → Off
  • Security
    • Block dangerous downloads → off
    • Warn about unwanted software → off
    • Block dangerous and deceptive content → off
    • Query OCSP → off (potentially UNSAFE!)
• Home
  • Homepage and new windows → Blank page
  • New tabs → Blank page

# Autocompletion in url bar should *not* connect to google
browser.urlbar.searchSuggestionsChoice = false
browser.urlbar.speculativeConnect.enabled = false

# localserver in url bar should not be translated to www.localserver.com
keyword.enabled = false
browser.fixup.alternate.enabled = false

# Disable WebRTC
media.peerconnection.enabled = false
media.peerconnection.video.enabled = false

# Disable gmp autoupdate, UNTESTED (disabled at compile-time)
media.gmp-manager.url = https://localhost

# Disable prefetching
network.dns.disablePrefetch = true
network.prefetch-next = false

# IDN phishing
network.IDN_show_punycode = true



network.http.referer.hideOnionSource = true

# This breaks google docs!
network.http.referer.spoofSource = true

browser.send_pings = false

# Disable clipboard control from JS
dom.event.clipboardevents.enabled = false

# Disable APIs used for fingerprinting
dom.webaudio.enabled = false
dom.battery.enabled = false
geo.enabled = false

media.navigator.enabled = false

# Disable captive portal
network.captive-portal-service.enabled = false
# The key above seems to be ignored in some versions, so remove the captive portal address
captivedetect.canonicalURL = ""

browser.ping-centre.production.endpoint = ""
browser.newtabpage.activity-stream.telemetry.ping.endpoint = ""


# https://wiki.mozilla.org/Privacy/Privacy_Task_Force/firefox_about_config_privacy_tweeks
privacy.firstparty.isolate = true
privacy.resistFingerprinting = true

# extension blocklists
extensions.blocklist.enabled = false

# extensions automatic update
extensions.systemAddon.update.enabled = false

# disable requests to search.services.mozilla.com/...
browser.search.geoSpecific.Defaults = false

# https://firefox.settings.services.mozilla.com/v1/buckets settings fetching?
services.settings.server = ""

# some websocket telemetry
dom.push.enabled = false

# ?
app.normandy.enabled = false

# ? investigate GET https://services.addons.mozilla.org/api/v3/addons/search/?guid=defau...
# 
extensions.systemAddon.update.enabled = false
services.sync.engineStatusChanged.addons = false

New Account setup wizard sends your e-mail domain to Mozilla. To add an account without this feature, select File → Offline → Work offline.

When you uncheck “Allow Thunderbird to send technical and interaction data to Mozilla”, it sends the following request to Mozilla:

POST /submit/telemetry/4e0009de-f8dc-4aad-8b07-30011f7622de/deletion-request\
/Thunderbird/78.7.1/default/20210203182138?v=4 HTTP/1.1
Host: incoming-telemetry.thunderbird.net
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1

{
  "type": "deletion-request",
  "id": "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXX",
  "creationDate": "2021-02-10T18:55:32.926Z",
  "version": 4,
  "application": {
    "architecture": "x86-64",
    "buildId": "20210203182138",
    "name": "Thunderbird",
    "version": "78.7.1",
    "displayVersion": "78.7.1",
    "vendor": "",
    "platformVersion": "78.7.0",
    "xpcomAbi": "x86_64-gcc3",
    "channel": "default"
  },
  "payload": {
    "scalars": {}
  },
  "clientId": "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXX"
}

When you open an attachment (tested with PDF), the following request is sent, leaking username, profile name, attachment filename and attachment SHA-256 hash (as raw binary data in the middle):

POST /safebrowsing/clientreport/download?key=%GOOGLE_SAFEBROWSING_API_KEY% HTTP/1.1
Host: sb-ssl.google.com
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1

00000000  4e 6d 61 69 6c 62 6f 78  3a 2f 2f 2f 68 6f 6d 65  |Nmailbox:///home|
00000010  2f 6a 65 6e 64 61 2f 2e  74 68 75 6e 64 65 72 62  |/jenda/.thunderb|
00000020  69 72 64 2f XX XX XX XX  XX XX XX XX 2e 64 65 66  |ird/XXXXXXXX.def|
00000030  61 75 6c 74 2f 4d 61 69  6c 2f 4c 6f 63 61 6c 25  |ault/Mail/Local%|
00000040  32 30 46 6f 6c 64 65 72  73 2f 49 6e 62 6f 78 12  |20Folders/Inbox.|
00000050  22 0a 20 ac a6 20 97 00  fa aa c6 15 80 ed b0 be  |". .. ..........|
00000060  5d 60 dd 49 64 4d b8 0c  9a e4 af 46 5b b6 ca b4  |]`.IdM.....F[...|
00000070  5b 09 e3 18 ff f4 0d 22  52 0a 4e 6d 61 69 6c 62  |[......"R.Nmailb|
00000080  6f 78 3a 2f 2f 2f 68 6f  6d 65 2f 6a 65 6e 64 61  |ox:///home/jenda|
00000090  2f 2e 74 68 75 6e 64 65  72 62 69 72 64 2f XX XX  |/.thunderbird/XX|
000000a0  XX XX XX XX XX XX 2e 64  65 66 61 75 6c 74 2f 4d  |XXXXXX.default/M|
000000b0  61 69 6c 2f 4c 6f 63 61  6c 25 32 30 46 6f 6c 64  |ail/Local%20Fold|
000000c0  65 72 73 2f 49 6e 62 6f  78 10 00 30 01 4a 25 50  |ers/Inbox..0.J%P|
000000d0  6f 74 76 72 7a 65 6e c3  ad 20 6f 62 6a 65 64 6e  |otvrzen.. objedn|
000000e0  c3 a1 76 6b 79 20 31 35  31 30 37 35 36 34 2d 31  |..vky 15107564-1|
000000f0  2e 70 64 66 50 00 5a 05  65 6e 2d 55 53           |.pdfP.Z.en-US|

To disable this, remove browser.safebrowsing.downloads.remote.url in about:config. Link to source where this happens.

Checks for updates even when the main app is not running. Same as described here.

This update checking does not respect network.proxy.http settings, but connect straight to the network, i.e., a standard intercepting proxy setup won't see it, it won't go through Tor etc.