User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:69.0) Gecko/20100101 Firefox/69.0

Steps to reproduce:

1. Go to this website: https://regex101.com/
2. Select ECMAscript in the left pane
3. Type in a regular expression containing a look-behind:
   (?<=1)2345
4. Type in this Test String:
   12345

Actual results:

This causes a pattern error in Firefox 69, but it works fine in Chromium 76.

I'm complaining because I cannot see support coming soon either:
https://caniuse.com/#feat=js-regexp-lookbehind

In what year will Firefox fully support the 2018 specification?

Expected results:

The 2018 specification supports look-behind assertions (?<=):
http://www.ecma-international.org/ecma-262/9.0/index.html#prod-Assertion

Therefore the code in this site should work in both Firefox and Chromium. This has been working in Chromium for over a year.

Hi,

This seems to be an enhancement.
However, I am assigning a component to this issue in order to involve the development team and get an opinion on this. If it's not the correct component please feel free to change it.

Thanks for the report.