I can see some pretty strong effects (and false positives) from what seem to be TLB misses. On my system, on Firefox, the L2 size is not detected correctly if transparent huge pages are enabled, but on Chromium it is. I'd like to take a closer at what's going on, but the tooling for performance-related debugging in browsers seem to be more or less missing. I've opened a pull request for some fixes to the C implementation though.