glassofcode

This is very lightweight, just few lines of code to remove storefront credit.

Remove built by storefront

This is very lightweight, just few lines of code to remove storefront credit.

wp-centrics

This plugin lets you easily edit the footer credit text for Storefront theme from customizer. No need for any code.
The original copyright text will be replaced by one or two widgetitzed areas, then you can put on it any widget: image, text, menu, etc.
This plugin will work only on <a href="https://wordpress.org/themes/storefront" rel="ugc">Storefront theme</a> WooCommerce theme.
Features:
<ul>
<li>Replace the Storefront copyright text by one (fullwidth) or two (two columns) sidebars (widgetitzed areas)</li>
<li>Place on the new footer sidebar(s) everything what you want, through widgets: logo, menus, text, html, etc.</li>
<li>Choose text align on every area: centered, left, right</li>
<li>Manage widgets nicely through customizer in the wordpress way, as any other sidebar</li>
<li>Format the menus in copyright in one line, or keep it in the standard sidebar menu look and feel.</li>
<li>You still can use the upper footer sidebars that come with Storefront, this plugin REPLACE the copyright with new one(s).</li>
</ul>
How to use:
<ol>
<li>Navigate to Customizer page under Appearance.</li>
<li>Find the Footer Section.</li>
<li>Under the Footer section, scroll down and you will find the alignment and menu style preferences.</li>
<li>Switch to the Widgets Section.</li>
<li>You will find a two new ones: Copyright Content Left and Copyright Content Right</li>
<li>Place on it the content as you need, by adding widgets</li>
<li>Leave the right content empty to make the left fullwidth (you will see the difference if you choose centered align)</li>
</ol>

Change Copyright for Storefront using Widgets – Change Storefront copyright text with menus, logos, html, etc.

Replace the footer credit text for WooCommerce Storefront theme easily from customizer through widgets! Put anything you need!

Remove built by storefront vs Change Copyright for Storefront using Widgets – Change Storefront copyright text with menus, logos, html, etc.