Could it be that you've got antitracking mechanisms enabled? Noscript, enhanced tracking protection or something else? They could very well prevent Firefox from

Could it be that you've got antitracking mechanisms enabled? Noscript, enhanced tracking protection or something else? They could very well prevent Firefox from accessing said APIs Edit: never mind, I just checked some, and they're all not supported according to caniuse. Interesting to see Firefox used to support battery api, but was removed for public consumption as of 52 due to privacy concerns.