That has nothing to do with Firefox properly downloading files. Your link has to do with a security bulletin regarding out of date Android devices being vulnerable to attacks.
Totally, but in a comparison of vulnerabilities it is much different to compare flaws in apps versus the default software included in the system. The former is a vulnerability to a very small percentage of users whereas the latter applies to literally every device. It also relies heavily on the App store acceptance policies, the ability to install apps not through the app store, and the competence of the developers making those apps.