I just benchmarked both Firefox and Chromium on my desktop using Speedometer 2.1. Each browser was configured as out of the box, with no extensions, and with a blank profile:

FF (114.0.1): 101 +- 1.9 Chromium (114.0.5735.198): 94.5 +- 2.2

FF (115.0.2): 104 +- 2.4 Chromium (115.0.5790.90): 101 +- 2.6

Machine Specs: Intel i5-3470 @ 3.2 GHz, 16 GB DDR3, 128 GB SSD. Linux kernel 6.1.38 (latest longterm branch) on Arch.