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Since today I noticed a problem in one of the webapps running on my server, in that it reported the timezone wrong - but only on Firefox

And indeed, checking in the console:

Intl.DateTimeFormat().resolvedOptions().timeZone

delivers

Etc/GMT-1

What's this supposed to mean? I am in a GMT+1 (+2 when counting currently active daylight savings time) timezone. On Chrome, the above command correctly returns Europe/Vienna.

OS: Windows 10, Firefox version: 59.0.2 (64 bit) with Add-Ons: NoScript, PrivacyBadger, uBlock Origin (tried with add-ons deactivated, no change), Chrome 65.0.3325.181 (64-Bit)

Is this a Firefox bug (though as far as I can tell Firefox was not updated in the past few days, and the problem only started today)? In the webapp also nothing changed as far as I can tell, so I suspect this to be a Firefox issue somehow (though I have no idea how Firefox gets to this "wrong" timezone info). Or is the timezone actually correctly referencing a time 2 hours ahead of UTC? And is the webapp mabye wrong in not recognizing this properly? I'm fresh out of ideas.

Searching in google hasn't brought up any recent hints regarding this (only some outdated ones, e.g.: Incorrect timezone in Firefox, compared to Safari, using javascript Date(), https://support.mozilla.org/de/questions/1191823). I also can't find anything else pointing at unusual timezone readings currently in Firefox, so I'm really wondering where this is coming from!

UPDATE:

To be honest, I have no idea what timezone firefox reported before - the actual problem I have is that the webapp (owncloud), when run in Firefox, reports not knowing the time zone specification - the message translates to "unknown timezone specification Etc/GMT-1. Falling back to UTC". The times are then 2 hours behind what I would expect them to be (which makes sense as current europe/vienna or europe/berlin time is 2 hours ahead of UTC). Not knowing how to interpret Etc/GMT-1 might be an issue on owncloud's part, but it has worked up until a few days ago, and still continues to work on Chrome...

More info as requested by Matt Johnson below:

>tzutil /g
W. Europe Standard Time

>echo %TZ%
%TZ%

Registry: TimeZoneInformation registry key content

I suppose I get Europe/Vienna instead of Europe/Berlin since I have configured to be located in Austria?

Addendum: I only get this behavior so far only on a single Windows 10 machine. On another Linux machine running Firefox, I do not see this behavior. I yet have to check on another Windows 10 machine

codeling
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2 Answers2

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There are two separate questions here:

Etc/GMT-1
What's this supposed to mean? I am in a GMT+1 ...

The tz database identifiers of the form Etc/GMT±* deliberately have an inverted sign than the usual forms we expect under ISO 8601. That is, they are in terms of positive values being West of GMT, rather than positive values being East of GMT. This is covered both in the Wikipedia article on the tz database, and in the commentary in the tz database itself.

Thus, it does indeed align with the current GMT+1 offset of your time zone. However, it doesn't reflect any DST of GMT+2.

... On Chrome, the above command correctly returns Europe/Vienna. ... Is this a Firefox bug?

That depends. What is your OS time zone set to? You said you are running Windows 10. Though Europe/Vienna maps to W. Europe Standard Time, the primary (001) mapping for that would be Europe/Berlin - so it's a bit odd that you would get Europe/Vienna unless there is something else influencing the result.

It is possible you have stumbled upon a bug, but it's also possible you have customized or corrupted time zone settings on your OS.

Please supply (via edit of your question) the values of:

  • The output of the tzutil /g command on the command line.
  • The value (if any) of a TZ environment variable (echo %TZ%)
  • All the values under this registry key (screenshot would be best): HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation

That will help identify the problem further. I will edit my answer accordingly. Thanks.

Matt Johnson-Pint
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I stumbled upon similar issue. It turned out that the user has time zone with the summer time support set in windows, but he deliberately disabled the summer time. I guess it creates a custom time zone not supported by IANA list, so it ends up with the Etc/GMT-1.

Birbone
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