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Firefox built-in PDF viewer stuck in light mode when privacy.resistFingerprinting is enabled

Firefox PDFs
Paul replied
Xinyue Wang
Xinyue Wang

Hi everyone,

After enabling `privacy.resistFingerprinting = true` in `about:config`, I noticed that Firefox’s built-in PDF viewer (`pdf.js`) is always displayed in **light mode**, even though my system and browser themes are both dark.

I understand that RFP forces `prefers-color-scheme: light` to prevent fingerprinting, but this also affects internal components like the PDF reader. Unfortunately, the PDF viewer doesn’t provide a manual dark mode toggle.

Is there any **official or safe workaround** that allows keeping RFP enabled while still having the PDF viewer use dark colors?

Thanks!

Hi everyone, After enabling `privacy.resistFingerprinting = true` in `about:config`, I noticed that Firefox’s built-in PDF viewer (`pdf.js`) is always displayed in **light mode**, even though my system and browser themes are both dark. I understand that RFP forces `prefers-color-scheme: light` to prevent fingerprinting, but this also affects internal components like the PDF reader. Unfortunately, the PDF viewer doesn’t provide a manual dark mode toggle. Is there any **official or safe workaround** that allows keeping RFP enabled while still having the PDF viewer use dark colors? Thanks!

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Paul
Paul
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Hi

The fingerprinting resistance is based on presets to try to achieve that aim and may not always lead to a configuration you would prefer for browsing.

An overview of a number of the settings are at https://support.mozilla.org/en-US/kb/resist-fingerprinting and I would avoid about:config if possible.