Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
No where does it say "on US soil" or "for US Citizens," and that is absolutely 100% by design based on the founding fathers philosophy which can be read in the declaration of independence.
It states plainly and unqualified "make no law abridging the freedom of speech." This both asserts that there is a freedom of speech that exists outside of the government and that congress shall make no law abridging it.
In their philosophy, the government purposefully doesn't grant the right to freedom of speech, because the founding fathers argument was that their, and all people's, natural god given (literally) rights are why they were justified in rebelling against the British government -- that rights exist outside of, and above, the government.