SUMMARY

Bit of an odd one. When watching a full screen Youtube Video, the mouse is smaller at rest. When you move the mouse, it becomes the correct size. It also makes the picture shift/jump a pixel (or two). Might be a fractional scaling thing? I have two 1440p monitors, and using a factor of 150%, and using Firefox native Wayland. 

STEPS TO REPRODUCE
1. Open YouTube Video in Firefox
2. Move mouse
3. Notice mouse size changes, and video jumps slightly

OBSERVED RESULT
Cursor changes sizes, and video jumps/shifts.

EXPECTED RESULT
Cursor should be the system setting and not change. Video should not move/jump.

SOFTWARE/OS VERSIONS
Arch Linux
Operating System: Arch Linux 
KDE Plasma Version: 5.27.8
KDE Frameworks Version: 5.110.0
Qt Version: 5.15.10
Kernel Version: 6.5.3-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 24 × AMD Ryzen 9 5900X 12-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: AMD Radeon RX 6900 XT

Firefox: 117.01, Wayland

Additional comments:

Could very well be Firefox itself, sure is certainly a bit of a paper cut on Wayland.