Firefox for Android
Firefox for Android before version 27
The random Profile Directory Name is written to the Android System Log (logcat) in various locations. For instance, upon Firefox launch, the following data is written:
D/GeckoProfile( 4766): Found profile dir: /data/data/.../files/mozilla/24pd90uh.default
In Android 4.0 and below, the Android log can easily be read by all applications including malicious ones by acquiring the READ_LOGS permission.