Does increasing zoom in tor browser give me a unique fingerprint?

Sometimes I struggle with my declining vision and feel the need to increase magnification of pages in the tor browser. For example, this forum is easier to read if I increase the zoom in my browser.

Does this affect my fingerprinting risk? If so, how does it affect it differently based on the security level I choose (safe, safer, safest)?

Would it be better for me to use a magnifying glass and put it up to the screen if I need to read things better? Are there other things that I could do that would be safer? Or is it safe for me to increase magnification in the browser?

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zoom, along with system scaling, devicePixelRatio, dpi, layout.css.devPixelsPerPx, default text size (there’s an option in setting to use larger text and/or larger default zoom) … etc … all affect the measurement of almost everything, so your fingerprint is altered

There’s no easy answer. If you need larger sizes, then use larger sizes - the internet has to be usable for you (meanwhile we have ideas on how to improve this)

read this: Increasing text size without increasing fingerprinting? · Issue #235 · mullvad/mullvad-browser · GitHub

if I increase the zoom in my browser.

how do you plan to do this? Your easiest solution is to just go to Settings > General > Zoom > Default zoom (optionally keep just zoom text). I wouldn’t mess with anything else TBH. At least this way you’re likely to be the same as some others since it’s front facing in the UI

Feel free to zoom in and out on individual sites, what matters is the default zoom level when loading (which we reset on each new site/tab - i.e reset to your default zoom level, as per settings)

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In addition, you can try out tools such as https://coveryourtracks.eff.org/, https://www.amiunique.org/, JavaScript Browser Information - BrowserLeaks . None of them seem to be checking “zoom level” directly: only screen size.

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TL;DR looks like yes, but I don’t know the extent

I don’t know much detail about how Tor Browser works, but checking devicePixelRatio in console shows that it’s always at 2. So perhaps there is some protection in this regard?

But you do have to remember that zoom level indirectly affects your screen size as it appears to the website (size on the monitor remains unchanged, but there are fewer pixels fitting into the view), and I believe even the “Safest” setting can’t save you from that because media queries can be used to detect screen size:

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you can just use TZP and the entire screen section will recalculate on desktop in real time on resize (manually with the window or by zooming)

this is just the screen/metrics and not all the other affected items - and it depends on how something is measured - for example, when enumerating fonts, the sizes in my test are preset at specific px sizes. So unless you know how something is collected and why, don’t assume you can read the results.

anyway, the screen section is a good example of how all those factors (zoom, devicepixelratio, dpi, etc etc) affect everything = subpixel entropy

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