In the manifest.json file I have set the following: "web_accessible_resources": [ "template.html" ] Then used the following command to get the url browser.runtime.getURL('template.html') Which results in the following as expected: safari-web-extension://40C1D308-F374-4C87-98C8-D9E9A4AD7945/template.html However, when trying to fetch the file from within the script I get : Failed to load resource: The requested URL was not found on this server. And when pasting it as a url in safari I get : Safari cannot open the page because the address is invalid. The template.html file exists in the same folder as the manifest.json file. I've even tried placing it in a folder called html, then using the following with wildcard, and that doesn't work either. "web_accessible_resources": [ "html/*.html" ]