Closed Bug 1965900 Opened 3 months ago Closed 3 months ago

ALT Key does not work when resisting fingerprinting

Categories

(Core :: Privacy: Anti-Tracking, defect)

Product:
Core
Component:
Privacy: Anti-Tracking
Version:
Firefox 139
Platform:
Desktop
Windows 11
Type:
defect

Tracking

()

Status:
RESOLVED DUPLICATE of bug 1598862

People

(Reporter: Catt0s, Unassigned)

References

(
URL
)

Details

(Keywords: 64bit, privacy)

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:139.0) Gecko/20100101 Firefox/139.0

Steps to reproduce:

Notes:

  • Mozilla Support post, for context: https://support.mozilla.org/en-US/questions/1511441
  • This issue did not occur on my stable 138.0.1 instance. It has been occurring for several months, throughout versions on my Developer Edition instance.
  • ALT+CLICK works fine, but no keyboard modifiers with ALT work.
  • Issue persists in Safe Mode
  • Using a JS key tester, the instance the bug is on does not show that ALT was ever pressed.
  1. Open Firefox Developer Edition
  2. Open a website that uses the ALT modifier in conjunction with other keys (Such as google sheets)
  3. Test out the relevant keyboard shortcuts

Actual results:

The keyboard shortcuts behave as if

Expected results:

The keyboard shortcuts should work as intended. For example, "Ctrl + Alt + Shift + C" becomes "Ctrl + Shift + C"

Attempting MozRegression with the profile.

Flags: needinfo?(mozilla_bog)
URL: https://support.mozilla.org/en-US/que...
Flags: needinfo?(mozilla_bog)
Keywords: 64bit

(In reply to Catt0s:Catt0s from comment #1)

Attempting MozRegression with the profile.

Using MozRegression with the same profile, the same issue occured in e78a64baff46c8e9bee42350c1048c8569824619 (build from 2024-05-13).

Investigating, it appears to be caused by privacy.resistFingerprinting being set to true

Keywords: privacy
OS: Unspecified → Windows 11
Hardware: Unspecified → Desktop
Summary: ALT Key does not work when using other modifier keys → ALT Key does not work when resisting fingerprinting
Component: Untriaged → Privacy: Anti-Tracking
Product: Firefox → Core

Hello! Thank you for submitting this issue I have tried to reproduce the issue on my end but unfortunately I wasn't able to with firefox 140.0a1(2025-05-13) on Ubuntu 22.04 and Windows 10
Could you please answer the following questions in order to further investigate this issue?

  1. Does this issue happen with a new profile? Here is a link on how to create one: https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles
  2. Does this issue happen in the latest nightly? Here is a link from where you can download it: https://www.mozilla.org/en-US/firefox/channel/desktop/
  3. Do you have any addons installed? If yes could you please list them?
Flags: needinfo?(mozilla_bog)

(In reply to Negritas Sergiu, Desktop QA from comment #3)

Hello! Thank you for submitting this issue I have tried to reproduce the issue on my end but unfortunately I wasn't able to with firefox 140.0a1(2025-05-13) on Ubuntu 22.04 and Windows 10
Could you please answer the following questions in order to further investigate this issue?

  1. Does this issue happen with a new profile? Here is a link on how to create one: https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles
  2. Does this issue happen in the latest nightly? Here is a link from where you can download it: https://www.mozilla.org/en-US/firefox/channel/desktop/
  3. Do you have any addons installed? If yes could you please list them?
  1. I created a new profile, turned on the flag in question, restarted Firefox, and the bug occurred.
  2. Indeed, if I use the latest nightly and enable the flag in question, the bug occurs.
  3. I do have addons installed, though the issue still occurs in Troubleshooting Mode. It also occurs in Nightly, which has no extensions installed. Experimenting on Stable (138.0.1) I was able to reproduce it on my existing profile.

Here is a list of extensions on that profile anyway:

Name: Add-ons Search Detection // Type: extension // Version: 2.0.0 // Enabled: true // Location: app-builtin-addons // ID: addons-search-detection@mozilla.com
Name: Archive Page // Type: extension // Version: 0.9.0 // Enabled: true // Location: app-profile // ID: {5b22cb75-8e43-4f2a-bb9b-1da0655ae564}
Name: ClearURLs // Type: extension // Version: 1.27.3 // Enabled: true // Location: app-profile // ID: {74145f27-f039-47ce-a470-a662b129930a}
Name: Decentraleyes // Type: extension // Version: 3.0.0 // Enabled: true // Location: app-profile // ID: jid1-BoFifL9Vbdl2zQ@jetpack
Name: DownThemAll! // Type: extension // Version: 4.13.1 // Enabled: true // Location: app-profile // ID: {DDC359D1-844A-42a7-9AA1-88A850A938A8}
Name: Fluffle // Type: extension // Version: 1.0.1 // Enabled: true // Location: app-profile // ID: {bd9ba7c9-2e9d-4a06-bb5a-7589d686760f}
Name: Form Autofill // Type: extension // Version: 1.0.1 // Enabled: true // Location: app-builtin-addons // ID: formautofill@mozilla.org
Name: New Tab // Type: extension // Version: 139.0.0 // Enabled: true // Location: app-builtin-addons // ID: newtab@mozilla.org
Name: Picture-In-Picture // Type: extension // Version: 1.0.0 // Enabled: true // Location: app-builtin-addons // ID: pictureinpicture@mozilla.org
Name: Privacy Badger // Type: extension // Version: 2025.3.27 // Enabled: true // Location: app-profile // ID: jid1-MnnxcxisBPnSXQ@jetpack
Name: SmartUpscale // Type: extension // Version: 1.4.1 // Enabled: true // Location: app-profile // ID: smart-upscale@tanalin.com
Name: Tampermonkey // Type: extension // Version: 5.3.3 // Enabled: true // Location: app-profile // ID: firefox@tampermonkey.net
Name: uBlock Origin // Type: extension // Version: 1.63.2 // Enabled: true // Location: app-profile // ID: uBlock0@raymondhill.net
Name: Web Archives // Type: extension // Version: 7.0.1 // Enabled: true // Location: app-profile // ID: {d07ccf11-c0cd-4938-a265-2a4d6ad01189}
Name: Web Compatibility Interventions // Type: extension // Version: 139.13.0 // Enabled: true // Location: app-builtin-addons // ID: webcompat@mozilla.org
Name: Whenplane Widget // Type: extension // Version: 2.1.0 // Enabled: true // Location: app-profile // ID: {d7efb617-4782-4ca1-841e-f1fde210896b}
Name: Dark // Type: theme // Version: 1.3.3 // Enabled: true // Location: app-builtin // ID: firefox-compact-dark@mozilla.org
Name: Feedbro // Type: extension // Version: 4.16.3 // Enabled: false // Location: app-profile // ID: {a9c2ad37-e940-4892-8dce-cd73c6cbbc0c}
Name: Tree Style Tab // Type: extension // Version: 4.1.6 // Enabled: false // Location: app-profile // ID: treestyletab@piro.sakura.ne.jp
Name: Wayback Machine // Type: extension // Version: 3.2 // Enabled: false // Location: app-profile // ID: wayback_machine@mozilla.org
Name: Firefox Alpenglow // Type: theme // Version: 1.5 // Enabled: false // Location: app-builtin // ID: firefox-alpenglow@mozilla.org
Name: Light // Type: theme // Version: 1.3.2 // Enabled: false // Location: app-builtin // ID: firefox-compact-light@mozilla.org
Name: System theme — auto // Type: theme // Version: 1.4.1 // Enabled: false // Location: app-builtin // ID: default-theme@mozilla.org
Flags: needinfo?(mozilla_bog)

[Tracking Requested - why for this release]:

status-firefox138: --- → ?
status-firefox139: --- → ?
status-firefox140: --- → ?

(In reply to [:Catt0s] from comment #5)

[Tracking Requested - why for this release]:

Ope did not mean to do that

Please allow me to restate the problem with currently known information, since the initial report contained information found to be inaccurate.

Summary

  1. Bug occurs when privacy.resistFingerprinting is set to true.
  2. Bug allows Alt+Click to work, but no Alt+[key] combinations register that Alt is pressed. Ctrl and Shift work fine.
  3. Bug persists in troubleshooting mode and in new profiles that have the flag in question enabled.
  4. Bug is present in Stable 138.0.1, Beta 139.0b7, 140.0a1 (2025-05-13), 128.01a
  5. Alt shortcuts outside of websites (For example, built-in FireFox shortcuts) appear to work as intended.

Steps to Reproduce:

For demo purposes, an easy way to test if this bug occurs is to open Google Sheets and use the keyboard shortcut ctrl+alt+shift+; to insert the current date and time. When the bug occurs, Alt will not register, and only the time will be inserted. This bug does occur on other websites - you can use jeffersonscher/keyvents to view key events, where Alt is not activated.

  1. Demo functionality for comparison.
  2. Open Firefox and navigate to about:config and search privacy.resistFingerprinting
  3. Set privacy.resistFingerprinting to true
  4. Restart FireFox
  5. Attempt to use a website's keyboard shortcut that involves the Alt key.

Expected behavior:

Alt+[key(s)] shortcuts from websites register.

Actual behavior:

Alt+[keys(s)] registers on websites as [key(s)]

Thank you for investigating this further and narrowing it down. This sounds like the expected behavior for RFP - we do modify how shortcut keys work to make a user's keyboard layout appear consistent and not leak the underlaying layout. This affects modifier keys.

I am not certain if this can be improved without leaking the keyboard layout, but I do know that we don't have any plans to investigate it - this aspect (and pref) is actually owned by Tor, so we wouldn't make a change there without them driving it.

For Firefox we would direct you to Fingerprinting Protection (privacy.fingerprintingProtection) which is the supported mode for Firefox. RFP is not a supported configuration and we don't really recommend it: https://support.mozilla.org/en-US/kb/resist-fingerprinting

Blocks: fingerprinting-breakage
No longer blocks: fingerprinting-breakage
Status: UNCONFIRMED → RESOLVED
Closed: 3 months ago
Duplicate of bug: 1598862
Resolution: --- → DUPLICATE
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