Bugzilla

(In reply to Tom Schuster (MoCo) from comment #9)
> Did you restart Firefox after setting the pref?

I did. I just retested, and that pref actually **does** avoid this issue under one specific set of conditions.  Starting with a fresh profile in about:config filtered for "resist"...
(1) Set `privacy.resistFingerprinting.testing.setTZtoUTC` to `true`
(2) Set `privacy.resistFingerprinting` to `true`
(3) Load the attached testcase (https://bugzilla.mozilla.org/attachment.cgi?id=9327566), or just directly execute `new Date()` in web console for about:config

If I do this, then I do see a `GMT+0000 (Coordinated Universal Time)` presentation of the datestamp.

However: if I swap the order of steps 1 and 2, OR if I restart Firefox after setting the prefs, then I see my local timezone.

So there seems to be some statefulness based on whether `privacy.resistFingerprinting.testing.setTZtoUTC` was enabled, at the moment that `privacy.resistFingerprinting` goes from `false` to `true`.

> I do want to remove this pref [the setTZtoUTC one] and code as soon as possible however.

Yeah, I only mentioned it because it seemed like it might've been a "belt-and-suspenders" way to work around this.

(In reply to Tom Schuster (MoCo) from comment #9)
> Did you restart Firefox after setting the pref?

I did. I just retested, and that pref actually **does** avoid this issue under one specific set of conditions.  Starting with a fresh profile in about:config filtered for "resist"...
(1) Set `privacy.resistFingerprinting.testing.setTZtoUTC` to `true`
(2) Set `privacy.resistFingerprinting` to `true`
(3) Load the attached testcase (https://bugzilla.mozilla.org/attachment.cgi?id=9327566), or just directly execute `new Date()` in web console for about:config

If I do those^ steps in precisely the right order, then I do see a `GMT+0000 (Coordinated Universal Time)` presentation of the datestamp.

However: if I swap the order of steps 1 and 2, OR if I restart Firefox after setting the prefs, then I see my local timezone.

So there seems to be some statefulness based on whether `privacy.resistFingerprinting.testing.setTZtoUTC` was enabled, at the moment that `privacy.resistFingerprinting` goes from `false` to `true`.

> I do want to remove this pref [the setTZtoUTC one] and code as soon as possible however.

Yeah, I only mentioned it because it seemed like it might've been a "belt-and-suspenders" way to work around this.