I updated Librewolf to 128.0.3-2 as usual, on start there's 5 sec of empty transparent window, then it falls back to WebRender (Software) in about:support, it does spit some stuff to dmesg:
[ 42.398344] Renderer[5496]: segfault at 2f4 ip 000076ac70ebee8c sp 000076ac69c0a6b0 error 4 in libxul.so[64bde8c,76ac6d3d8000+5c0d000] likely on CPU 6 (core 0, socket 0)
[ 42.398359] Code: 00 00 ff 11 48 85 c0 74 0a 48 85 db 0f 95 80 56 01 00 00 48 83 c4 08 5b 41 5e c3 cc cc cc f3 0f 1e fa 41 57 41 56 53 48 89 fb <8b> 86 f4 02 00 00 85 c0 75 2c 49 89 f7 bf 10 00 00 00 ff 15 fc 3d
[ 42.911327] Renderer[5564]: segfault at 2f4 ip 000074f2bf0bee8c sp 000074f2b5efe6b0 error 4 in libxul.so[64bde8c,74f2bb5d8000+5c0d000] likely on CPU 1 (core 1, socket 0)
[ 42.911338] Code: 00 00 ff 11 48 85 c0 74 0a 48 85 db 0f 95 80 56 01 00 00 48 83 c4 08 5b 41 5e c3 cc cc cc f3 0f 1e fa 41 57 41 56 53 48 89 fb <8b> 86 f4 02 00 00 85 c0 75 2c 49 89 f7 bf 10 00 00 00 ff 15 fc 3d
[ 44.201214] Renderer[5619]: segfault at 2f4 ip 00007212028bee8c sp 00007211fb4756b0 error 4 in libxul.so[64bde8c,7211fedd8000+5c0d000] likely on CPU 0 (core 0, socket 0)
[ 44.201225] Code: 00 00 ff 11 48 85 c0 74 0a 48 85 db 0f 95 80 56 01 00 00 48 83 c4 08 5b 41 5e c3 cc cc cc f3 0f 1e fa 41 57 41 56 53 48 89 fb <8b> 86 f4 02 00 00 85 c0 75 2c 49 89 f7 bf 10 00 00 00 ff 15 fc 3d
[ 48.848893] Renderer[5919]: segfault at 2f4 ip 00007501864bee8c sp 000075017f08e6b0 error 4 in libxul.so[64bde8c,7501829d8000+5c0d000] likely on CPU 2 (core 2, socket 0)
[ 48.848914] Code: 00 00 ff 11 48 85 c0 74 0a 48 85 db 0f 95 80 56 01 00 00 48 83 c4 08 5b 41 5e c3 cc cc cc f3 0f 1e fa 41 57 41 56 53 48 89 fb <8b> 86 f4 02 00 00 85 c0 75 2c 49 89 f7 bf 10 00 00 00 ff 15 fc 3d
[ 49.420155] Renderer[6256]: segfault at 2f4 ip 00007b821c8bee8c sp 00007b821379d6b0 error 4 in libxul.so[64bde8c,7b8218dd8000+5c0d000] likely on CPU 2 (core 2, socket 0)
[ 49.420178] Code: 00 00 ff 11 48 85 c0 74 0a 48 85 db 0f 95 80 56 01 00 00 48 83 c4 08 5b 41 5e c3 cc cc cc f3 0f 1e fa 41 57 41 56 53 48 89 fb <8b> 86 f4 02 00 00 85 c0 75 2c 49 89 f7 bf 10 00 00 00 ff 15 fc 3d
[ 53.251627] Renderer[6299]: segfault at 2f4 ip 000079e14e6bee8c sp 000079e1473f56b0 error 4 in libxul.so[64bde8c,79e14abd8000+5c0d000] likely on CPU 0 (core 0, socket 0)
[ 53.251639] Code: 00 00 ff 11 48 85 c0 74 0a 48 85 db 0f 95 80 56 01 00 00 48 83 c4 08 5b 41 5e c3 cc cc cc f3 0f 1e fa 41 57 41 56 53 48 89 fb <8b> 86 f4 02 00 00 85 c0 75 2c 49 89 f7 bf 10 00 00 00 ff 15 fc 3d
[ 55.880344] Renderer[6668]: segfault at 2f4 ip 00007464eacbee8c sp 00007464e3a176b0 error 4 in libxul.so[64bde8c,7464e71d8000+5c0d000] likely on CPU 0 (core 0, socket 0)
[ 55.880355] Code: 00 00 ff 11 48 85 c0 74 0a 48 85 db 0f 95 80 56 01 00 00 48 83 c4 08 5b 41 5e c3 cc cc cc f3 0f 1e fa 41 57 41 56 53 48 89 fb <8b> 86 f4 02 00 00 85 c0 75 2c 49 89 f7 bf 10 00 00 00 ff 15 fc 3d
[ 57.170052] Renderer[6723]: segfault at 2f4 ip 00007990192bee8c sp 0000799011e226b0 error 4 in libxul.so[64bde8c,7990157d8000+5c0d000] likely on CPU 6 (core 0, socket 0)
[ 57.170061] Code: 00 00 ff 11 48 85 c0 74 0a 48 85 db 0f 95 80 56 01 00 00 48 83 c4 08 5b 41 5e c3 cc cc cc f3 0f 1e fa 41 57 41 56 53 48 89 fb <8b> 86 f4 02 00 00 85 c0 75 2c 49 89 f7 bf 10 00 00 00 ff 15 fc 3d
Downgrading to 128.0.3-1 fixes the issue. I run x11/i3wm + 560.31.02 nvidia drivers.