I honestly don't rightly recall which FW version stopped supporting the ALT fonts trick, but it's quite possible that this doesn't work on FW 4.x, and I just wasn't aware of it (the current check to disable that in the plugin is FW >= 5.0, because that I was sure of ;p).
Someone actively using alt fonts on a similar device may be of more help

. If it turns out it really isn't supported, ping me, and I'll update the plugin.