Anchor from subpage does not work in Firefox

Hi there,
when i click on an anchor on a subpage to get back to the mainpage the browser scrolls down to nearly to the end of the mainpage.
I'm using the slider Plug in at the top of the mainpage. Maybe there is the problem. Anyone here who can help?

Got a URL to look at?

yes

but it is password protected.
And i can't post it here

Can you PM me a temp account?

Well, i'm not sure what the problem is. It's not Grav-related though as I have the same issue even if is save the file as HTML.

It must be something with the HTML itself. Or it could be some JS that is interfering and scrolling the page itself. I'm not sure. Sorry.

Yes, in my opinion it is the slider js. i guess firefox does first all the pictures. picture under picture, jumps then to the anchor and after that gets the js from the slider