I seem to be getting the same errors on Solaris. And funny - I want to use W::M::F as well *and* don't feel optimistic about forcing this. Code hasn't been touched since 2007.

Actually to make the test pass in 20-plugin-json.t I just added double quotes in this line (my diffs):

diff 20-plugin-json.t ../../MozRepl-0.06-882RqE/t/20-plugin-json.t 
17c17
<     is($repl->json({ source => MozRepl::Util->javascript_value({a =>
+ 1, b => 2})}), q|"{"a":1,"b":2}"|);
---
>     is($repl->json({ source => MozRepl::Util->javascript_value({a =>
+ 1, b => 2})}), q|{"a":1,"b":2}|);
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But I have no idea if this makes sense. This more 'it hurts when I do that - so I am not doing that!'