Solaris: Thunderbird and Firefox 1.5

I've installed Firefox 1.5, Solaris 8, SPARC, works just fine.

Thunderbird (1.02, Solaris 8, SPARC), however, can't open a link anymore:

    Firefox is already running, but is not responding. To open a new
    window, you must first exit the existing Firefox process, or restart
    your system.

Uh, that doesn't seem right somehow -- Firefox opens a Thunderbird 
window but not the other direction.

These are the packages from Mozilla.org.

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Thank you,

Solucient LLC