Rated 5 out of 5 stars

It's work, but unfortunately at the xubuntu 14.04 i can't see numbers of unread messages at tray.
Found already build version here: https://github.com/foudfou/FireTray/issues/242, work fine for me.
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@JokeRTrG:
For TB 60.
git clone https://github.com/firetray-updates/FireTray
cd FireTray/src
make build
ls ../build-*/*.xpi # <-- your xpi, ready to be installed