Packages with the system-harfbuzz use flag

mail-client / thunderbird : Thunderbird Mail Client

Use the system-wide media-libs/harfbuzz and media-gfx/graphite2 instead of bundled.

www-client / chromium : Open-source version of Google Chrome web browser

Use system harfbuzz instead of the bundled one.

www-client / firefox : Firefox Web Browser

Use the system-wide media-libs/harfbuzz and media-gfx/graphite2 instead of bundled

www-client / seamonkey : Seamonkey Web Browser

Use the system-wide media-libs/harfbuzz instead of bundled