Webpage button will not respond to getElementById

I have tried many different ways but cannot get a button to respond on a webpage from VBA. Code I am trying:

Set btn = IE.document.getElementById("gs-address-go")
btn.FireEvent ("onmousedown")
btn.FireEvent ("onclick")
btn.Focus
btn.Click

HTML extract of the object:

<button id="gs-address-go" class="b-btn bold go-btn" onclick="$('#splash-get-walkscore-form').submit(); return false;" aria-label="Go"><span class="icon big-search"></span></button>

Any help appreciated