User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:71.0) Gecko/20100101 Firefox/71.0

Steps to reproduce:

Localization settings set to Australia in Windows.

1. Go to a page with SSL (e.g. google.com)
2. Open "Page Info" -> "Security" -> "View Certificate"
3. The date fields are incorrectly localized (e.g. Validity)

Actual results:

Validity shows in the US Date format (MM/DD/YYYY):
Not After 11/29/2019, 7:21:24 AM (Australian Eastern Standard Time)

Expected results:

Should show the Australian (or UK) date format (DD/MM/YYYY):
Not After 29/11/2019, 7:21:24 AM (Australian Eastern Standard Time)

I assume you're using Firefox in American English (en-US). According to this, you should be getting en-AU regional settings since they're both en
https://firefox-source-docs.mozilla.org/intl/locale.html#regional-preferences

Can you provide a screenshot of your Windows regional settings?

the date should be formatted using Services.intl.DateTimeFormat. I don't see any formatting here - https://searchfox.org/mozilla-central/source/toolkit/components/certviewer/content/certviewer.js#117

I saw intl.DateTimeFormat() was used for the timezone, I assumed it was used for that too. What's interesting is that it's localized for me (Italian), but the tooltip is not.

I've attached my windows region settings above.

The priority flag is not set for this bug.
:wleung, could you have a look please?

For more information, please visit auto_nag documentation.

Needs more investigation :)

This is also an issue on MacOS 10.14.6 Firefox 71.0
Date format should be 3/1/2020 and 5/10/2020 based on my regional settings which I'll attach in separate screenshot

And here are my MacOS regional settings. See how the example date format is d/m/yy not m/d/yy.

Duping to bug 1601841, because there is some investigation there.