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hidden canvas fingerprint blocker plugins are setting off tracking alarm using fresco

edited January 2015 in Fresco
chrome exentions like CanvasFingerprintBlock or firefox extensions like CanvasBlocker, that are supposed to block hidden canvas tracking, complain about hidden canvas tracking or even block fresco from working.

there was one user complaining about that, so i tried to reproduce it.
just so that i understand: is the querying of a hidden canvas used to position the lightbox, is it essential and would there be an option to work around that?

two plugins that complain about the fresco demo page:

https://addons.mozilla.org/en-US/firefox/addon/canvasblocker/
https://chrome.google.com/webstore/detail/canvasfingerprintblock/ipmjngkmngdcdpmgmiebdmfbkcecdndc

Comments

  • edited February 2015
    Canvas is used to create a drag image that shows up when dragging to save. That's not something that can be disabled.

    Fresco uses a feature test to see if Canvas can be used before actually using it. If a plugin decides to disable the Canvas API, it should make sure that feature tests checking for the existence of the Canvas API fail.

    The plugins you've mentioned probably kill whatever Canvas does without letting the browser know they've disabled Canvas, this breaks feature testing. Something that should be fixed in the plugin so developers can work around the things they've disabled. Plugins that properly inform the browser and take feature testing into account won't have these issues.
  • thanks. that’s about what i think about it.
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