Just an update on this.
Although this is clearly a bug in El Capitan / Chrome (and I've reported it as such to both), we have actually worked around this in XenForo 1.5.
Fun fact: It's caused by the results attribute on search elements:
Rich (BB code):
<input type="search" results="5" />
We have effectively removed all uses of this attribute throughout all templates.
When those changes roll out here later, the site should become usable in Chrome on OS X 10.11 again. Which will be much to
@Jeremy and my relief
Couple of exceptions, however; this attribute is still in use in some Gallery and Resource Manager pages so you might expect to still see issues on these pages, though we will likely fix the issue there, too, eventually.