I used multipart replace in firefox for streaming data for years with no download spinner. I couldn't use it in chrome because chrome always seemed to have some weird bug where 'frames' (of data in my case) were delayed.
I was disappointed when they were unceremoniously ripped out, but yes, websockets are better.
Ok, I believe you, it's been over 10 years since I tried it :-) Maybe I was thinking of the forever iframe, where a regular application/javascript document had content added to it incrementally over time.
It is actually pretty bizarre. If you point Chrome at a .jpeg that does multipart/replace it will stall, giving you roughly 0.2 fps. Point it at a. .html that contains an <img> tag and it works fine. Found this out while hacking on Hawkeye: https://igorpartola.com/projects/hawkeye/
I was disappointed when they were unceremoniously ripped out, but yes, websockets are better.