I made myself an userscript that gathers certain data from websites I browse and stores them in cache on localhost. First I used to make standart cross-site HTTP XMLHttpRequests, however the firefox has implemented another XHR restriction that prevents me from doing so - mixed content blocking. However, [https://support.mozilla.org/en-US/kb/how-does-content-isnt-secure-affect-my-safety?as=u&utm_source=inproduct on firefox blog] I saw information, that HTTPS requests are considered safe and are not blocked. So I added security exception for localhost, and changed requests to https requests. (and even https requests from localhost to localhost behave that way) Now the requests are being sent properly, but no data are received from server. Why is that? How many security policies has firefox put in front of me? Oh and sorry guys, I've forgotten to specify error messages upon each situation: '''a)''' Cross-site http request: "''Blocked mixed content...''" Normal http request within localhost works. '''b)''' Cross-site and normal https request: "''Certificate not trusted beacuse its self signed''" '''c)''' Cross-site and normal https request with certificate exception: nothing. Not even a notice.''