Some notes that I have noticed. First, why does it seem that the V8 date parser is heavily inspired by the Windows date parser (https://devblogs.microsoft.com/oldnewthing/20200304-00/?p=10...)? EDIT: Apparently not, "new Date('Savvyday 29 Oatmeal 94')" is invalid both in Firefox and Chrome.

Second, I opened this in Firefox with the console open to answer these questions, and found these divergences (to summarize, Firefox is strict):

Question 14:

  new Date("12.1")

> "12.1" is interpreted as the date December 1st, and as before for dates with no year the default is 2001 because of course.

Firefox returns an Invalid Date object instead.

Question 16:

  new Date("12.-1")

> The dash here is ignored, so this is interpreted the same as "12.1".

Again, Firefox returns an Invalid Date object instead.

Question 19:

  new Date("maybe 1")

> "may" in "maybe" is parsed as the month May! And for some reason this expression cares about your local timezone, which happens to be BST for me right now.

Seems a broken record, but this is still an Invalid Date for Firefox.

Question 20:

  new Date("fourth of may 2010")

> "fourth of" is ignored, this is just parsing "may 2010" and again local timezone is important.

Ibid in Firefox.

Question 21:

  new Date("May 4 UTC")

> UTC is correctly parsed as a timezone.

No, Firefox is still not accepting this one.

Question 22:

  new Date("May 4 UTC+1")

> You can add modifiers to timezones and it works as you would expect.

Neither this one.

Question 23:

  new Date("May 4 UTC+1:59")

> It also supports minutes!

Firefox: Not really.

Final note: It parses Question 24 as you expect in Firefox. Which honestly, it shouldn't!