[Suggestion] Remove obsolete "contains" methods

[Moonchild]

Off-topic:

there where risks tend to 0 or just exposure has 0 impact on the user.

IMO. well informed users should have the power to decide what they want and how to use

While I agree to a point with that sentiment, removing all basic safeguards that are common sense is just as extreme as aiming for 0 vulnerabilities, ever.

You don't remove the railings from your stairs or gantries because you're careful walking on them, but also don't strap yourself in a harness that makes it physically impossible to ever fall. If you get my point.
Win XP at this point is like a railless gantry. Sure, you can use it safely if you have good balance, but if anything untoward happens you're pretty much screwed. I know there is a vocal minority of people who absolutely insist they want to keep using it out of some sense of desiring a never-changing computing environment, and that's why these forks endure. Does it make sense otherwise? Not really. I have no problem people wanting to use it in isolated environments either, but that's not the point of a modern browser, is it?

IOW: balance your safeguards. Don't go overboard in either direction.

[BenFenner]

I don't think we should do this without some kind of underlying security reason

If I am a web developer (and I happen to be one) and I target Pale Moon, I can be reasonably sure my web site will work on all contemporary browsers. Having these "legacy" (for lack of a better word) method aliases around when none of the other contemporary browsers support it anymore makes the (admittedly fanciful) practice of only targeting Pale Moon less effective.

Not that I expect this would ever effect me personally or professionally, but just wanted to voice this small point.

I can certainly see the argument for keeping them active, and I won't lose sleep over it either way.

[Moonchild]

I can be reasonably sure my web site will work on all contemporary browsers. Having these "legacy" (for lack of a better word) method aliases around when none of the other contemporary browsers support it anymore makes the (admittedly fanciful) practice of only targeting Pale Moon less effective.

It's always good practice to double-check in other browsers before publishing, of course. But I do get your point and it's why I generally do follow the standards and want to remove things that have been dropped when they are actually not supposed to be in use any longer.

I just don't see a point of quickly removing this particular one because of the potential impact. If people can do the leg work and investigate the scope of impact of this, then I am in a better position to know whether this should go or not, but I'm not just going by the flat "it has changed in the standard so should go" when it's a simple, and very widely-used function that was active for a long time in JS (and why I was actually against renaming it to begin with!). The longer and more widely something was active before it was removed, the longer of a "run out" period there should be after it's been dropped from the standard.