I really dislike calver for like libraries and apis. For something like Firefox it doesn't matter as much. But for a library? I want to know if this version has breaking changes.

I'm with you; I prefer date versioning for many things. Semver does work really well for things with exposed APIs; it's a stretch to justify using them with user tools, and especially GUI tools. Semver is used to great effect in Go - which is how it should be use: mainly by the language's module management system. Outside of that, it's human readable, but like XML, its main value is to machines, and only secondarily to humans.

Calendar versioning is far more human-oriented, and so more useful for things without exposed APIs or module tooling.