On windows you can speed chromium up by renaming it to chrome.exe so it gets special treatment by antivirus software.

Chromium's executable[1][2] is already named chrome.exe unless the builder goes out of their way to rename it. This can't be the reason.

1. https://download-chromium.appspot.com/ 2. https://ungoogled-software.github.io/ungoogled-chromium-bina...

That's incredibly dumb if true, but can't be the whole story because the difference is still present in the Linux stats.

Doesn't windows check the signature or something to decide if an application should be allowed to bypass antivirus? Seems like doing it based on the filename would be a pretty huge security hole.

Chrome tends to be built with a rather slow and stringent set of optimization extras like PGO that people tend to leave off in Chromium builds.

Probably PGO.

Even prebuilt Firefox tend to be faster than distro provided ones, at least at some point on the past.

Looks like the Arch repos do PGO on firefox: https://gitlab.archlinux.org/archlinux/packaging/packages/fi...