As someone with both Chrome and Firefox installed why should I click the Firefox button? I mean it's mostly the same but gives me out of memory errors.

Last time I tried it a thing saying "Refresh Firefox" popped up which I clicked and it wiped the extensions which I got back following some online help but lost completely I think the crypto keys in metamask - like https://www.reddit.com/r/Metamask/comments/14rcg6k/firefox_r...

Luckily I had backup elsewhere but it kind of freaked me out.

I've never seen Firefox use more memory than Chrome on modern versions. They're pretty on par.

It's far more likely that one of the many addons/extensions you had was the cause.

As for 'Refresh Firefox', it does exactly what it says it does - wipe a lot of your configuration to bring it closer to stock. It's intended as a way to show people new defaults and help clear out old, bloated configs. It shouldn't be used unless you know what you're doing.