Hey Support @RueNel,
Thanks for the reply (and the solution
) - crazy, I thought I tried what you suggested first and it hadn’t worked! Clearly I hadn’t had enough coffee yet that morning. That issue is all sorted now, thank you!
I do have a couple more questions though 
a) When using one page navigation to move around on a page, it looks as though the browser doesn’t take into account the height of the navigation bar, so often the top of the content is covered up.
For example, a user clicks a link with the URL #infoSection and the site scrolls down to that section. The top of the page lines up with the top of the #infoSection, but because the navigation bar is 200px high, the top 200px of the #infoSection is hidden behind it.
Is there any way to offset the one page navigation scrolling to account of the height of the navigation bar?
b) We are using the section separators extensively on our site (they are a great addition to the theme) but they often have a clear line between the body of the section and the separator. How can we remove this line? 
See the line in the orange section.
This final one is more of the general CSS question:
c) We have some formatting issues on Firefox associated with the headerbuilder. Is there a way to format a class just in one specific browser?
The problem is we have a logo in a bar in the header builder. On firefox the logo appears incorrectly, under the buttons below it (but it is displayed as intended on all other browsers). It seems that the margin which works on other browsers displays differently on firefox. Can we target one browser specifically with CSS?
Thanks for all your help,
Best Regards,
Andy