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Once you publish the changes, the favicon will display on your live Store Editor pages.
Once you publish your changes, the favicon will display on all of your checkout pages.
Tip: If you find that a Yahoo favicon is still in place of yours after the update, rename the favicon.ico file to something else such as favicon_new.ico then update the code in the HTML Head section of your site pages:
<link href="/favicon_new.ico" rel="shortcut icon" />