Regarding the news on Firefox Send being temporarily down, because of malware uploads, I figured that checking the hash at VirusTotal is a good indicator if the file in question should be allowed to be uploaded or not.
That seems like a decent enough feature to enable Firefox Send again,
Just to be clear, files that one is trying to upload at Firefox Send should not be uploaded to VirusTotal, just before uploading to Firefox Send, the has(md5/sha512), should be calculated, and VirusTotal should be queried if the file is know there, and if the file is a Virus.
VirusTotal API: https://developers.virustotal.com/reference