How do you search all iCloud email folders at once?

Hello,

I've just started using iCloud mail. For a variety of reasons, I have to access my emails from Firefox on my mac. I use the icloud.com site, however there is no obvious way to search through all of my folders.

For example:

I want to find an email from Andy which he sent me a few years ago.

I don't know which folder it's in, so I want to quickly search through all of them.

Is there any way to do this?

Thanks,

Oliver