Play a VP9 video in original Firefox ESR from SUSE and check hardware acceleration with intel_gpu_top (from rpm intel-gpu-tools). My Intel GPU Gen 9.5 (Kaby Lake) works well with intel-vaapi-driver.
If you need hardware acceleration for decoding H.264/AVC videos in Firefox ESR, recompile libavformat58_76 and libavcodec58_134 with H.264/AVC decode support. See:
Use a german to english translator like deepl.com.