The HTML changed in v760, instead of requiring users select a "go" button to proceed to the target forum, as soon as one is selected from the dropdown they're directed there now. If the target browser does not support javascript then a "go" button will be displayed.
This is the forum navigation system that's on the topic list and topic view pages. For comparison, here's the change from the v7.5 series that exists in the v7.6 series.
Old:
<select name="board" id="board" class="form-select">
-Forum Listing-
</select>
<input type="submit" name="Jump" value="Go" class="form-button" />
New:
<select name="board" id="board" class="form-select" onchange="this.form.submit()">
-Forum Listing-
</select>
<noscript><input type="submit" name="Jump" value="Go" class="form-button" /></noscript>
"Why"? Because it's a cleaner and more elegant approach.