Firefox flagging zipfile from HumbleBundle

I bought some software off of HumbleBundle and the files were zip files. When I tried getting the first zip file Firefox flagged it as having malicious content so I stopped trying to get the files and scanned my system.

I reached out to HumbleBundle and they assured me that their content would not have viruses or malware and that it is a false positive, but I am a little uneasy now

Not sure how I can safely know if Firefox is having these as false positives or not