@juraj.masiar thanks again for the insight and guidance. I tried out some new ideas based on the MDN Web Docs, but was not able to get it to work.
The additional complexity with this is that this CSS information is getting passed over to another Firefox addon. I am basically passing some custom CSS via a sendMessage, so unless the i18n is resolved to a fully qualified URL text BEFORE sending the message, I doubt the other addon would be able to use it. This might make sense as to why the fully qualified URL with the UUID in the string works, but the i18n version doesn’t.
I may have to stick with the Unicode solution (limited choices) or an external URL (would hate to hit someone’s posted PNG or figure somewhere to host it myself). I really thought stuffing the proper URL at runtime into a variable and passing it into url() would have worked. [“myURL” option below]
browser.runtime.sendMessage(ID, {
...
style: `
...
conditions item-to-style::after {
/* Works */
/* content: url("http://icons.iconarchive.com/icons/oxygen-icons.org/oxygen/24/Actions-document-encrypt-icon.png"); */
/* content: url("http://icons.iconarchive.com/icons/fatcow/farm-fresh/24/lock-icon.png"); */
/* content: url("moz-extension://32b76189-c6cf-43d0-af5c-e10691134da7/lock.png"); */
/* Doesn't work */
/* content: url(myURL); */
/* content: url(browser.runtime.getURL('/lock.png')); */
/* content: url(moz-extension://__MSG_@@extension_id__/lock.png); */
/* content: url(lock.png); */
/* content: url('/lock.png'); */
content: url("http://icons.iconarchive.com/icons/fatcow/farm-fresh/24/lock-icon.png");
}
`
});