Firefox

The problem is that it will sometimes remove parameters that aren't tracking parameters. It won't happen often, but if it happens, that can be really bad.
Just imagine someone copying a link, pasting it into a document and only noticing several months later, that the link doesn't anymore resolve to what they wanted.

If you install a plugin for this, then you'll know to check that the link still works before documenting it somewhere. But rolling this out as the default for millions of unsuspecting users, that is just an entirely different story...