1739194 - RFP breaks Color Scheme Simulation via DevTools

Status: NEW

(DevTools :: Inspector, defect, P3)

Description

[ConnorJC]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Firefox/91.0

Steps to reproduce:

1. Enable privacy.resistFingerprinting via about:config
2. Visit any website that supports the preferred-color-scheme media query (example: https://bugzilla.mozilla.org/)
3. Verify the website appears with light styling
4. Open devtools, attempt to simulate dark color scheme (click the moon icon in the inspector tab)

Actual results:

Page does not switch to dark color scheme

Expected results:

Page switches to dark color scheme (i.e. RFP should not interfere with DevTools testing tools)

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'DevTools::Inspector' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Comment 2

[Julian Descottes [:jdescottes]]

Check what is expected for color scheme media queries when resistFingerprinting is enabled.

Comment 3

[Alexandre Poirot [:ochameau]]

It is probably an issue for many things other than color scheme.
We do change the behavior of many web APIs when resist finger printing is enabled:
https://searchfox.org/mozilla-central/search?q=ShouldResistFingerprinting&path=&case=false&regexp=false

Regarding color scheme, it probably relates to this one check:
https://searchfox.org/mozilla-central/rev/88cd13997fb0747cdcd78638fc762ff2d75e1fc5/dom/base/Document.cpp#17628-17631

Comment 4

[ConnorJC]

Attachment: rfp-devtools-interference.patch

I can confirm moving this check before the RFP check fixes this issue and allows the devtools to override RFP. I believe this will also allow extensions to override the RFP setting (from the API in bug 1733461), but that behavior may be desirable anyways?

Comment 5

[Bruno Pagani]

Related: https://bugzilla.mozilla.org/show_bug.cgi?id=1732114 and https://bugzilla.mozilla.org/show_bug.cgi?id=1745453.

And yes, I would like that to work more generally than just with devtools.

Comment 6

[Julian Descottes [:jdescottes]]

If any decision comes up for Bug 1732114 we can reconsider, for now there's no clear action.

Comment 7

[Tom Ritter [:tjr]]

Like Bug 1826998 - the behavior of RFP as it interacts with Devtools is a very undefined, grey area. Some of that grey will need to be addressed since FPP is a supported feature, but for now we haven't overlapped any FPP things with Devtool breakage.