Steps to reproduce:

Consider https://chromium.github.io/octane/

Firefox 100 x86-64, native official Mozilla Linux build: roughly 40K points
SeaMonkey 2.53.12 x86 running under Wine x86: roughly 60K points.

Actual results:

The native x86-64 version is running ~33% (!!) slower than the "emulated" x86 version of SeaMonkey 2.53.12.

Expected results:

Versions used:

SeaMonkey 2.53.12: https://archive.mozilla.org/pub/seamonkey/releases/2.53.12/win32/en-US/seamonkey-2.53.12.en-US.win32.installer.exe

Firefox 100: https://ftp.mozilla.org/pub/firefox/releases/100.0/linux-x86_64/en-US/firefox-100.0.tar.bz2

The test is 100% reproducible. In both situations I used new profiles with no changes or any extensions installed.

I managed to reproduce this issue on Ubuntu 20.04 on Firefox 100, 101 and 102.
Setting this as New, updating the flags and waiting for the developer's opinion about it.
Edit: fixed a typo in the spelling.

I suspect this is due to divergence in JIT features. No direct performance impact as this is not on an actual website.

“SeaMonkey 2.53.12 uses the same backend as Firefox and contains the relevant Firefox 60.8 security fixes.” — https://www.seamonkey-project.org/releases/seamonkey2.53.12/

This is likely to be the difference between IonBuilder + TypeInference versus WarpBuilder.
While our focus moved away from benchmarketting, this is a problem which should be addressed by WatchTower.