In firefox you could set following:

dom.block_download_insecure = false
browser.fixup.fallback-to-https = false
security.insecure_field_warning.contextual.enabled = false
dom.security.https_only_mode = false
network.http.encoding.trustworthy_is_https = false

and may be some other for recent version, you eventually could get rid of that idiocy with "security" warnings.