There are two quick solutions.
The easiest is simply to...
1. Download the file in a different browser like Chromium or Chrome.
This is the best option if it's just the one file that's causing you problems but if it keeps happening over and over then this really isn't practical.
Also consider the future implications. It only tells you it's blocked the file after its been downloaded. Imagine you're five hours and 99% into downloading a vital 2GB file over a sluggish connection then suddenly that error pops up - you're gunna be mad.
2. Disable safebrowsing.
While this will get rid of the annoying warnings, it will also disable warnings when you're visiting dodgy sites, such as forgeries or phishing sites so it's not a decision to be taken too lightly.
On balance, for a Linux user with a bit of sense, I think it's not at all risky. However, if you're still worried consider downloading a good range of protective add ons such as Bitdefender.
Here's how to disable safebrowsing:
- Type "about:config" in the address bar.
- Click ok to all the Here Be Dragons warnings.
- Search for and set the following two values to false:
browser.safebrowsing.malware.enabled
4. Restart Firefox and download the file.
