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How to Block System Font Detection in Firefox ?

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Taking a look at the screenshot attached below you will see the librewolf browser which is a fork of firefox, blocks system font detection by default. How does librewolf do that? I hope by reading your reply i will be able to achive the same outcome with firefox. I'm also interested on how to block system local time readout/detection with firefox as i have so far not found a solution to this issue. As a privacy focused person i do not see any reason why any website would be interested in the timezone of my operatingsystem. This information is most likely not even necessary for functionality. From my knownledge the android browser named bromite (source: https://www.bromite.org/) does block timezone detection by default, since firefox is a privacy browser i fail to understand why this feature is not included to the settings tab.

PS: I'm not interested to making any suggestions anywhere, i want to modify firefox to block both system font and system timezone detection, any help is welcome...

Taking a look at the screenshot attached below you will see the librewolf browser which is a fork of firefox, blocks system font detection by default. How does librewolf do that? I hope by reading your reply i will be able to achive the same outcome with firefox. I'm also interested on how to block system local time readout/detection with firefox as i have so far not found a solution to this issue. As a privacy focused person i do not see any reason why any website would be interested in the timezone of my operatingsystem. This information is most likely not even necessary for functionality. From my knownledge the android browser named bromite (source: https://www.bromite.org/) does block timezone detection by default, since firefox is a privacy browser i fail to understand why this feature is not included to the settings tab. PS: I'm not interested to making any suggestions anywhere, i want to modify firefox to block both system font and system timezone detection, any help is welcome...
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Chosen solution

There are several layout.css.font-visibility prefs you can find on the about:config page that determine the visibility of the fonts.

  • layout.css.font-visibility.standard 3
  • layout.css.font-visibility.trackingprotection 3
  • layout.css.font-visibility.resistFingerprinting 1
  • layout.css.font-visibility.private 3
1 - only base system fonts
2 - also fonts from optional language packs
3 - also user-installed fonts

You can consider to enable "Resist Fingerprinting" but be aware that this can cause all kind or weird/unexpected issues with websites.

Using Resist Fingerprinting in Firefox has its disadvantages as this affects the user agent, but also places you in the UTC timezone and gives you rounded screen dimensions and can give font issues with locally installed fonts and disables site specific zoom. There are other ways like using extensions or Firefox Enhanced Tracking Protection to deal with specific details you want to block or change.

WARNING: modifying prefs directly via the about:config page can sometimes break Firefox or cause strange behavior, and there is no guarantee that this will keep working in future Firefox releases, so be cautious with modifying prefs if you aren't sure you understand their purpose. You should only do this if you know what you're doing.

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Chosen Solution

There are several layout.css.font-visibility prefs you can find on the about:config page that determine the visibility of the fonts.

  • layout.css.font-visibility.standard 3
  • layout.css.font-visibility.trackingprotection 3
  • layout.css.font-visibility.resistFingerprinting 1
  • layout.css.font-visibility.private 3
1 - only base system fonts
2 - also fonts from optional language packs
3 - also user-installed fonts

You can consider to enable "Resist Fingerprinting" but be aware that this can cause all kind or weird/unexpected issues with websites.

Using Resist Fingerprinting in Firefox has its disadvantages as this affects the user agent, but also places you in the UTC timezone and gives you rounded screen dimensions and can give font issues with locally installed fonts and disables site specific zoom. There are other ways like using extensions or Firefox Enhanced Tracking Protection to deal with specific details you want to block or change.

WARNING: modifying prefs directly via the about:config page can sometimes break Firefox or cause strange behavior, and there is no guarantee that this will keep working in future Firefox releases, so be cautious with modifying prefs if you aren't sure you understand their purpose. You should only do this if you know what you're doing.

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Thanks! Didn't know about the values 1-3.

Now the one thing left of concern to me is blocking websites from spying on my systemtimezone. Can this be done with firefox or with the operatingsystem itself? After all i know for a fact that the bromite android browser has this feature and it works. I noticed that disabling javascript blocks systemtimedetection, but it also basically renders the browsers useless for my purposes.. are there specific javascript config settings regarding systemtimezone detection? I really feel that when a website spys on my systemtimezone this is a breach of privacy as this goes beyond the browsers im using to view the website but instead directly access information about my system, im not ok with that... Using a virtualmachine just to fake systemtimezone cannot be the solution, this is ridiculous.

privacy.resistFingerprinting does not caused any issues for me.

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Edit: I marked this as solved, thanks again, about timezone let me open a new issue.

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