I tried web benchmarking on Firefox, but the CPU usage was over 90%. Compared to Chrome, the CPU usage less than 10%.
I notice clearly that FireFox hardware acceleration doesn't work with AMD GPU driver. Chrome and Steam work fine with default driver in Manjaro, but FireFox does not, despite hardware acceleration being active.
KDE Plasma Version: 5.18.4
Kernel Version: 5.6.3-2-MANJARO
GPU AMD Radeon RX5700
AMD Driver: "video-linux" as default driver