Menu behind header in FF

Hello, I’m a newb, and have set up a site

https://www.mcavoygardenservices.co.uk
Theme is Aeros.

The top menu is behind the header transparency in FF. It’s ok in chrome and IE.
I’ve tried all that I know how to, can anyone help?

I’ve tried adding z-indexes, padding and absolute positioning with some entertaining results, but no success.
I think the problem arose when I removed the original CSS link and image (which I didn’t want) replacing it with a logo. But now even if I remove the logo the problem persists in FF, even though it was working fine before I meddled with it (I’d say I’m an idiot, but we must often just try these things…).

Thank you in advance. If there’s anything else needed I’ll check this tomorrow. Free images of beer to anyone who helps.