Firefox has issues currently on M1, as well - uBlock Origin won't load, for example. Thankfully, that particular issue is fixable by disabling javascript.options.wasm and javascript.options.wasm_trustedprincipals in about:config as a temporary solution.
I fully expect these to be fixed, but it's clear it's gonna be a few weeks/months before everything runs right. If I were a non-technical user, I'd be returning it for an Intel Macbook.