Trying to download files with periods in their name will have everything after the first period truncated.
Many ways to trigger this but for the sake of testing try downloading these 2 files:
Actual file names are:
com.google.android.apps.messaging_4.7.056_(Kraken_RC13_xxxhdpi.arm64-v8a.phone)-47056249_minAPI21(arm64-v8a)(560,640dpi)_apkmirror.com.apk.
Caesium-wahoo-v3.6-b792615ced1b.zip
These are also the file names when downloaded on other browsers (Chrome, Firefox desktop, etc).
In fenix the downloaded file names are:
com.apk
Caesium-wahoo-v3.zip
Could https://github.com/mozilla-mobile/android-components/commit/b2a1f28277c91cfc2db0369d01b7572ccba8d001 be related?
This is a huge problem in my opinion as most apk downloads are named com.apk and files with version numbers in their name (e.g. v3.1.zip and v3.2.zip) also get the same name (v3.zip).


This will get fixed when we transition to the new Gecko download manager (#4296). I'll look into fixing it for the current download manager as well.
Fixed in Android Components 6.0.0