Mozilla, as well as Chrome and Safari, use Google’s “Safe Browsing” service, which warns users about potentially dangerous software on the web. Mozilla announced that starting with the next version of Firefox (48), its browser will be able to block both “potentially unwanted software” and “uncommon downloads.”
“Potentially unwanted software” is software that makes unexpected changes to your computer, such as collecting your personal information without your consent or making itself difficult to uninstall.
“Uncommon downloads,” as the name says, is not software that’s necessarily malicious; it's just not commonly downloaded. Blocking such software may trigger quite a few false positives, but Google’s Safe Browsing service blocks it by default because there’s the potential to block many more malicious files than safe ones.
For instance, phishing sites could make users believe they are downloading a popular program such as VLC, when in fact they are downloading a malicious file. The Safe Browsing service can detect that the file is not actually popular (as one would expect VLC to be) and block it. Users can still manually enable the download when it’s blocked, if they are certain the download is safe.
Improved User Interface
To make it easier to understand at first glance for users, Mozilla made a few improvements to the user interface for these warnings. The potentially unwanted and commonly downloaded software will be flagged with a yellow icon, whereas the files known to be malicious will be flagged with a red one. If it’s potentially unwanted or uncommon software, then the action button will be a folder so users can open it, or an "X" so users can delete it immediately.
Mozilla modified the Security options to reflect the new changes with the expanded protection against unwanted and uncommonly downloaded software, while allowing users to completely disable these new protections.
Firefox 48 is also supposed to arrive with the “Electrolysis” sandboxing feature enabled by default, so it looks like this version will bring quite a few security improvements. Firefox 47 came out in early June, so the new version should be out soon, considering Firefox’s six-week schedule.