Navbar dropdown menus stopped working in chrome & IE

[JamesAB]

I have a bizarre problem that is probably template related.

The dropdown menus in the navbar stopped working in chrome & IE, however they still work in Firefox.

If I switch from my styles to the "Default Style" they seem to work again.

How can I troubleshoot this?
What files or vBulletin components are needed to make the navbar dropdown menus function properly?

I tried simply copying the navbar tempate from the "Default Style" to my own style, but that didn't fix the problem.

Thanks for your help.

[MarkFL]

I would suspect there is some CSS class selector difference. Try inspecting the DOM to see if you can spot the difference between the two styles with regards to any selectors.

[JamesAB]

It seems to be related to the contents of headinclude

By converting back to the default from the "Default Style" it makes the menus work again.

I'll try to track down the differences now.

--------------- Added [DATE]1483806663[/DATE] at [TIME]1483806663[/TIME] ---------------

I think it turned out to be a javascript problem.
I had been using async when calling some scripts, but some browsers don't seem to like that anymore.

<script async type="text/javascript" src="$stylevar[yuipath]/yahoo-dom-event/yahoo-dom-event.js?v=$vboptions[simpleversion]"></script>
<script async type="text/javascript" src="$stylevar[yuipath]/connection/connection-min.js?v=$vboptions[simpleversion]"></script>

When I remove the async directive things seem to work in all browsers again.