In FireFox, you can pass the event object in as a parameter e.g.:
<div class="btn_view"><a href="#" onclick="toggle_visibility('all-avon',this, event);">VIEW TYRES</a></div>
function toggle_visibility (id,el, e)
(then use e.preventDefault, just to make it separate to window.event in IE etc)
Although, as you are using jQuery, I would suggest doing what Sergio mentioned above/below.