Texifier macOS, like all macOS applications, declares to macOS those file types which it can open by default. It does not declare those file types which it should open.

Very often macOS will be aware of multiple applications that can open a given file type, and it needs to choose one. Applications are unable to provide any type of priority here, so that choice will follow user preference if it is known, and at random if it is not.

If Texifier is opened by default for a file type you would rather open with another application, or another application is opened by default for files you would rather open with Texifier, this behaviour is customisable. It is a macOS level behaviour, and there is nothing we can do in Texifier itself to affect it.

Please follow the guide on Apple’s support pages on how to let macOS know what your preferred application is for any given file type.