/usr/share/iceowl/extensions/langpack-fy-nl@lightning.debian.org/chrome.manifest is in lightning-l10n-fy-nl 1:45.8.0-3~deb8u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | locale calendar fy-NL jar:chrome/fy-NL.jar!/locale/fy-NL/calendar/
locale lightning fy-NL jar:chrome/fy-NL.jar!/locale/fy-NL/lightning/
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