You must check cpu abi version, and change geckoview_library and geckoview_asset to match the abi.
http://ftp.mozilla.org/pub/mozilla.org/mobile/nightly/
From the link, you can download several kinds of geckoview library.
This is a sample.
[DIR] latest-mozilla-central-android-armv6/ 12-Dec-2013 11:50 -
[DIR] latest-mozilla-central-android-r7/ 12-Dec-2013 11:56 -
[DIR] latest-mozilla-central-android-x86/ 12-Dec-2013 11:56 -
[DIR] latest-mozilla-central-android/ 12-Dec-2013 11:56 -
In each folder, download geckoview_library and geckoview_asset.