noVNC relies on the browser to decode JPEG images, as that will most likely be massively faster than doing it in JavaScript. Unfortunately Firefox has some odd delay in returning the decoded result. Other browsers return the result pretty much right away, but Firefox takes tens of milliseconds. Throughput seems to be unaffected though, so the effect is primarily delayed, but not slowed down, rendering. That delay still could still cause queues to build up and confuse the congestion control. We haven't found a workaround yet. It doesn't seem to matter which method we use to wait for the image to load. Reported upstream: https://bugzilla.mozilla.org/show_bug.cgi?id=1304391
There is still some delay, but it's similar to Chrome now. The performance of running an entire noVNC playback test is also better on Firefox than Chrome now. Not sure if we need to care about this anymore. (Firefox can get even faster loading using newer APIs: https://github.com/novnc/noVNC/pull/1131)
The original issue seems to have resolved itself, so let's close this bug. We don't want it growing to some general performance investigation bug.
