[DiapDealer]

I'm not sure how FPS is relevant at all in xhtml rendering. There is no video playing. So there are no "frames" involved at all. Please stick with latency. And if you could provide the method with which you're able to accurately measure Sigil's Preview latency, that would be great too. So we can all compare apples to apples.

But regardless... Preview's supposed latency with hardware acceleration disabled is an entirely separate issue from memory leaks. Can you please confirm that disabling WebEngine's hardware acceleration stops the increasing memory use issue? Then maybe we can figure out why disabling hardware acceleration creates such noticeable latency on your hardware, but not on others'.

Can you also confirm that you have no global Qt environment variables set on your system (perhaps for other Qt programs or games) that could affect Sigil's behavior?