Bugzilla

(In reply to Tom Ritter [:tjr] from comment #4)
> I believe that this is working as intended.

Not exactly. `privacy.resistFingerprinting.pbmode` is documented as such (emphasis added by me):
# When the .pbmode pref is on, RFP or FPP will be **enabled in PBM**

In the STR here, I am at no point entering PBM, so it's surprising that there's any behavior-change from this pref being enabled.

Having said that: I did notice the code you linked to which notes "The frame rate is a global property", so it's presumably not possible to turn it off specifically for PBM windows.  But we could still only start throttling it when a PBM window is opened, perhaps?

(LayoutFrameRateFromPrefs is a dynamic function -- it does seem to be responsive to live changes to the pref, in a fresh profile without any fingerprinting prefs toggled.  So it seems conceivable that we could adjust it so that its `privacy.resistFingerprinting.pbmode`-specific behavior gets dynamically enabled when a Private Browsing window is opened.)

(In reply to Tom Ritter [:tjr] from comment #4)
> I believe that this is working as intended.

Not exactly. `privacy.resistFingerprinting.pbmode` is documented as such (**-emphasis added by me):
`# When the .pbmode pref is on, RFP or FPP will be **enabled in PBM**`
https://searchfox.org/mozilla-central/rev/76b13c585e575cf273fd05ab3b48a1532c1d1faa/modules/libpref/init/StaticPrefList.yaml#13114,13116

In the STR here, I am at no point entering PBM, so it's surprising that there's any behavior-change from this pref being enabled.

Having said that: I did notice the code you linked to which notes "The frame rate is a global property", so it's presumably not possible to turn it off specifically for PBM windows.  But we could still only start throttling it when a PBM window is opened, perhaps?

(LayoutFrameRateFromPrefs is a dynamic function -- it does seem to be responsive to live changes to the pref, in a fresh profile without any fingerprinting prefs toggled.  So it seems conceivable that we could adjust it so that its `privacy.resistFingerprinting.pbmode`-specific behavior gets dynamically enabled when a Private Browsing window is opened.)

(In reply to Tom Ritter [:tjr] from comment #4)
> I believe that this is working as intended.

Not exactly. `privacy.resistFingerprinting.pbmode` is documented as such (**-emphasis added by me):
`# When the .pbmode pref is on, RFP or FPP will be **enabled in PBM**`
https://searchfox.org/mozilla-central/rev/76b13c585e575cf273fd05ab3b48a1532c1d1faa/modules/libpref/init/StaticPrefList.yaml#13114,13116

In the STR here, I am at no point entering PBM, so it's surprising that there's any behavior-change from this pref being enabled.

Having said that: I did notice the code you linked to which notes "The frame rate is a global property", so it's presumably not possible to turn it off specifically for PBM windows.  But we could still only start throttling it when a PBM window is opened, perhaps?  (which would affect normal windows too, but at least it'd be a bit more scoped and understandable-to-users due to the temporal connection between the frame-rate change and the private browsing window opening.)

(LayoutFrameRateFromPrefs is a dynamic function -- it does seem to be responsive to live changes to the pref, in a fresh profile without any fingerprinting prefs toggled.  So it seems conceivable that we could adjust it so that its `privacy.resistFingerprinting.pbmode`-specific behavior gets dynamically enabled when a Private Browsing window is opened.)