CSS width transition using background-image

Question

I've set up a website using a background-color, to expand the full width of the screen. This worked fine as a placeholder, but my original intent was to use a background image to slide in. I've looked up how to do this, and that it isn't supported by FireFox. This was >4 years ago and I can't find any new sources on this site or any other that this may have changed (4 years is a long time!). Is there an existing, supported method to do this now?

Here's the original question for reference. CSS3 background image transition

Thanks for answering!

Answer 1

Answered by Showdev in comments. He uses transitions to solve the issue.