Javascript doesn’t work, only through WP

I’m at a loss. Hope someone might have an idea for me.

I don’t use javascript very often, but I have a situation that calls for it. I’m using two js files to create a tab effect on a page.

The script and html/css works fine if I use it as a stand alone.

When I include in my sidebar, it suddenly doesn’t work at all anymore.

I placed both js files in a folder called /js in my theme.

The files are tabs.js and prototype.js

I call both of the js through the head of my document as is:
<script src="<?php bloginfo('url'); ?>/wp-content/themes/mythemename/js/tabs.js" type="text/javascript" ></script>

I include a bit more of js that actually triggers the script as follows:

<script type="text/javascript">
		<!--
Event.observe(window,'load',function(){
        $$('.tabs').each(function(tabs){
            new Control.Tabs(tabs);
        });
    });
    //-->
</script>

I read through https://codex.www.ads-software.com/Using_Javascript#Using_Multiple_Javascript_Files_inside_one_post_or_page and spend a couple hours sifting through this forum, haven’t found a thing.

I tried removing most WP calls from the head, removed the actual post stuff and only loading the sidebar. To no avail.

There’s obviously a conflict somewhere. But I can’t, for the life of me, figure out what might be not happy.

Unfortunately, I don’t have a live site to show you at the moment, it’s all local. Early on the design process of the site, but if this tab feature won’t work, I have to abandon the design

Thanks for any assistance.