VectorTile renderMode vector Firefox regression

[keepitrealsimple]

Describe the bug
Firefox gets pretty much stuck when using VectorTile renderMode vector. It looks like GPU utilization goes 100% and won't come down. Tested on Windows and Mac. Chrome, Edge and Safari seems to work ok but maybe get a little bit slower. Issue is present on OL 9.1.0 and it was working fine in OL 8.2.0.

To Reproduce
Steps to reproduce the behavior:

1. See attachment zip -> Extract -> npm install -> npm start (It is fork from https://openlayers.org/en/latest/examples/canvas-tiles-tms.html with added renderMode:vector)
2. Zoom all the way up -> zoom all the way in -> zoom all up -> zoom all in -> Try to move map
3. Browser becomes unresponsive

Expected behavior
Map should work without jamming browser with normal usecase

ol-910-firefox-mvt-rendermode-bug.zip

[ahocevar]

Thanks for the report. I can reproduce the issue. I'm working on improvements.