I got some findings, here is the code:

sub js_call_to_perl_struct {
    my ($self,$js,$context) = @_;
    $context ||= '';
    $self->{stats}->{roundtrip}++;
    my $repl = $self->repl;
    if (! $repl) {
        # Likely during global destruction
        return
    };
    my $queue = join '',
                     map( { /;$/? $_ : "$_;" } map { s/\s*$//; $_ } @{
+ $self->queue });
        
    @{ $self->queue } = ();

    #warn "<<$js>>";
    my @js;
    if ($queue) {
        push @js, $self->repl_API('q', $queue);
    };
    push @js, $self->repl_API('ejs', $js, $context );
    $js = join ";", @js;
    
    if (defined wantarray) {
        #warn $js;
        # When going async, we would want to turn this into a callback
        my $res = $self->execute_command($js);
        $res =~ s/^(?:\.+\>\s+)+//g;
        while ($res !~ /\S/) {
            # Gobble up continuation prompts
            warn "No result yet from repl";
            $res = $self->execute_command(";"); # no-op
            $res =~ s/^(?:\.+\>\s+)+//g;
        };
        my $d = $self->to_perl($res);
        if ($d->{status} eq 'ok') {
            return $d->{result}
        } else {
            croak ((ref $self).": $d->{name}: $d->{message}");
        };
    } else {
        #warn "Executing $js";
        # When going async, we would want to turn this into a callback
        # This produces additional, bogus prompts...
        $self->execute_command($js);
        ()
    };
};
[download]

Where in the code :

my $res = $self->execute_command($js);
[download]

$js is:

 repl.ejs("
var f=function() {\n       
var wm = Components.classes[\"@mozilla.org/appshell/window-mediator;1\
+"]\n.getService(Components.interfaces.nsIWindowMediator);\n
var win = wm.getMostRecentWindow('navigator:browser');\n        
if (! win) {\n// No browser windows are open, so open a new one.\n    
+      
win = window.open('about:blank');\n };\n        
return win.getBrowser()\n    }\n;\n;
f",""
);
[download]

In firefox7.0, after command execution, the return value $res is:

"{"status":"ok", "result":{"result":1,"type":"function"} }"

But in firefox 8,it returns something different: "8.0!"?!? Thats why it fails always. Any solutions?