Firefox based that on data from Google's Safe Browsing project. I'm not sure what's going on with that data, but several others users are reporting false positives as well. It could be that large hosting sites are tagged for hosting one piece of malware and this affects the reputations of other files on those sites which are not malware, but that's just a guess.

For the future, the developers are considering an option to override the block and get the file anyway (similar to the option in Chrome). It probably will be at least a few months before that appears because security-sensitive changes take time to design.

For now, if you think these files actually are safe, you could do one of the following when you discover a blocked download:

(1) Download the file using a different browser (yikes)

(2) Download the file using a downloader add-on that bypasses this security check. I heard about this in another thread but haven't tried it myself (and also, I don't know which add-ons to trust for this!).

(3) Disable the Safe Browsing feature temporarily to get the file, then turn it back on. There is a checkbox in the Options (Preferences) dialog:

"3-bar" menu button (or Tools menu) > Options > Advanced

Sorry, for Linux: "3-bar" menu button (or Edit menu) > Preferences > Advanced

On the Security tab, it's the "Block reported attack sites" checkbox. The other checkbox relates to phishing sites and I don't think it affects downloads.

Sorry I don't have a better suggestion at the moment.

Thank you @jscher2000 for answer. I use option 3 in the future for downloading from this site.

See also:

• http://www.ghacks.net/2014/11/19/bypass-firefoxs-blocked-may-contain-a-virus-or-spyware-message/