odoo-addons/muk_web_theme-19/muk_web_theme/templates/web_layout.xml

<?xml version="1.0" encoding="UTF-8"?>
<odoo>

    <template id="layout" inherit_id="web.layout">
	    <xpath expr="//link[@rel='shortcut icon']" position="before">
	    	<t 
		    	t-set="x_icon" 
		    	t-value="x_icon or '/web/image/res.company/%s/favicon' % request.env.company.id"
	    	/>
	    </xpath>
    </template>
    
</odoo>