User agents that work with ff3 XPI:
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Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.13) Gecko/2009080315 Ubuntu/9.04 (jaunty) Firefox/3.08

User agents that work with ff3+ XPI:
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Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.0.12) Gecko/2009072110 Fedora/3.0.12-1.fc10 Firefox/3.0.12