Is it possible to recover a blocked Firefox download?

I download a huge .zip file with the latest Firefox browser on Windows 8.1 but after finishing the download this error came up:

Blocked: May contain a virus or spyware

There isn't a virus in it because the file is from a trusted friend. Do I need to download the .zip again or is there a way to unblock it or getting out of a temp folder or something like that?

This is caused by the integration with Google's safe-browsing features where it blocks certain file names that are considered to be dangerous - yes including .zip because the list is constantly up-to-date so sometimes certain .zip files can somehow be matched. For whatever reason certain free file hosting sites (which your friend may have used) have a tendency to trigger this and one way I've seen this is by appending .exe to the Content-Disposition header and under certain conditions the download dialog will still show that as .zip but the browser had already assumed it to be harmful because the name matched something it blocked.

In Firefox case, it will just delete the file, so it is no longer recoverable. The only recourse is to disable this feature and this is possibly dangerous. To do so, open up about:config (type that out in the address bar and press Enter), if this is your first time you may have to click the button promising to be careful. In the search box, find browser.safebrowsing.malware.enabled and double-click on that, which should flip the value from true to false and bold the whole statement. The malware protection will be turned off completely in Firefox. You can then try to download the file again and it should no longer be blocked. Remember to undo this change by flipping the switch back to true once you are done downloading on your second attempt.

Alternatively, use Google Chrome which will provide this blocking feature, however it does not delete the file but rather rename the file to something harmless looking and mark that download as blocked in the download dialogue, with the option to unblock the file (by opening the download dialogue using Ctrl-J) which will rename the download file back to what it was originally.