Try downloading Firefox from Mozilla, run firefox-bin from the folder and see if you have the same issue. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Are your ffmpegs current? I'm on a rolling version, so your versions may differ. It would help if you provided examples or show a screen recording. I'm not seeing any issues on any of the sites. Are you using X11 or Wayland?

Operating System: openSUSE Tumbleweed 20230610 KDE Plasma Version: 5.27.5 KDE Frameworks Version: 5.106.0 Qt Version: 5.15.9 Kernel Version: 6.3.6-1-default (64-bit) Graphics Platform: X11 Processors: 8 × Intel® Xeon® CPU E3-1535M v6 @ 3.10GHz Memory: 62.2 GiB of RAM Graphics Processor: Mesa Intel® HD Graphics P630 Manufacturer: HP Product Name: HP ZBook 17 G4

How do I know if ffmpegs are current? How would I update them?

Try this https://www.cyberciti.biz/faq/how-to-install-ffmpeg-on-fedora-linux-using-dnf/

From this google search.