FrostWire for Android (Basic and Plus) version 1.9.9 and later work on Android devices with an operating system version 4.4 or later, which means Android 4.3 Jelly Bean is no longer supported.
A low number of active devices and/or users on an Android version 4.2 and below was the main reason for dropping the support. The development of the app's code was significantly hindered by being forced to support such an old operating system and many functions could not be coded properly (or at all) to support the new operating systems.
We highly recommend users to upgrade the Operative System whenever the device's hardware allows for it. You can check for Android updates in your device's Settings > About phone > Software info > Update > Software Update