From treo Addicts:

For those of you who use Thunderbird, Firefox’s email companion, there is an extension available to sync your contacts with your Palm device. PalmSync winds up replacing the Palm address book Hotsync conduit. Unfortunately its only available for Windows users. You will want to have at least Thunderbird 1.0.2 installed (1.0.6 was recently released).

I have not tried this yet, but it looks pretty interesting. It’s a Windows-only conduit for syncing your Palm address book with the Thunderbird address book. Too bad I no longer have a Windows machine at work so I could only use this at home.