I had that with Safari for a while but not with foxfire. It is really stinks to have to keep signing in!

https://www.makeuseof.com/how-to-enable-disable-cookies-iphone/

Could be accidental, of course. I presume you are not the hacker type that blocks cookies on a site by site basis ( I do ) or who clears history and data in "Settings" for safari periodically.

Hope this helps.

Check your cookie settings per the article linked.

Good luck.

to have the option to do that, just to clear cookies, which I haven’t done in a while.

Presuming safari on a recent ios.

I do stuff accidentally.

A lot.

https://discussions.apple.com/thread/8658504?sortBy=best

That's easy to do by tapping the two overlapping squares at the bottom right. (Tap and hold to get a menu)

Private browsing clears cookies when a tab is closed.

and will see what happens. Never even knew it was there. Thank you for taking the time to help.

I did a bunch of computer support in my heyday.

So glad that it cured the problem.