I have similar results when running the code in the Firefox devtools console, however, running these benchmarks in a dedicated webpage does not show the results.

When using a dedicated web page, I see results which are in the same ranges as NodeJS and Chrome: (not comparable, as running on different hardware)

   Started data Local (original) foo.html:120:11
  Finished data locality test run in  8.6800 ± 1.3095  ms. foo.html:144:11
   Started data Non-local (original) foo.html:120:11
  Finished data locality test run in  38.9400 ± 1.6195  ms. foo.html:144:11
   Started data Local foo.html:120:11
  Finished data locality test run in  6.6600 ± 1.1390  ms. foo.html:144:11
   Started data Non-local foo.html:120:11
  Finished data locality test run in  38.6400 ± 1.5861  ms. foo.html:144:11
   Started data Non-local (sorted) foo.html:120:11
  Finished data locality test run in  12.1800 ± 1.8334  ms. foo.html:144:11
   Started data Local (object) foo.html:120:11
  Finished data locality test run in  14.4500 ± 1.1492  ms. foo.html:144:11
   Started data Non-local (object) foo.html:120:11
  Finished data locality test run in  49.0000 ± 1.6576  ms. foo.html:144:11
   Started data Non-local (sorted array of indices) foo.html:120:11
  Finished data locality test run in  53.8500 ± 2.9725  ms.

I opened a bug against the devtools console of Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1647276