Bugzilla

Noticed when testing in Tor Browser.

## Steps to reproduce

Using Firefox with "ar" locale:

1. In "about:config" set `privacy.spoof_english` to `2`.
2. Restart.
3. Visit https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/datetime-local#basic_uses_of_datetime-local

## Result

From left to right, the unfilled datetime input shows: picker; AM/PM input; date input; time input.

After entering an hour, the layout switches to: picker; date input; time input; AM/PM input.

## Expect

The order and direction should remain the same and follow the spoofed en-US direction: date input; time input; AM/PM input; picker.

Note, the fact that the placeholders use "ar" rather an "en-US" is a separate issue, which should have a bug on bugzilla soon.

## Cause

I think the problem is that datetime input [uses the app locale direction](https://searchfox.org/mozilla-central/rev/9bb5d5f55da6cc7163dd93825c25609b769822f9/toolkit/content/widgets/datetimebox.js#145) to set the "dir" attribute. Rather than using the direction associated with the `mLocales[0]`.

Noticed when testing in Tor Browser.

## Steps to reproduce

Using Firefox with "ar" locale:

1. In "about:config" set `privacy.spoof_english` to `2`.
2. Restart.
3. Visit https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/datetime-local#basic_uses_of_datetime-local

## Result

From left to right, the unfilled datetime input shows: picker; AM/PM input; date input; time input.

After entering an hour, the layout switches to: picker; date input; time input; AM/PM input.

## Expect

The order and direction should remain the same and follow the spoofed en-US direction: date input; time input; AM/PM input; picker.

Note, the fact that the placeholders use "ar" rather an "en-US" is a separate issue: bug#1880108.

## Cause

I think the problem is that datetime input [uses the app locale direction](https://searchfox.org/mozilla-central/rev/9bb5d5f55da6cc7163dd93825c25609b769822f9/toolkit/content/widgets/datetimebox.js#145) to set the "dir" attribute. Rather than using the direction associated with the `mLocales[0]`.