There is a mistake in the addonchat_popup template highlighted in red:
Code:
$stylevar[htmldoctype]
<html xmlns="http://www.w3.org/1999/xhtml" dir="$stylevar[textdirection]" lang="$stylevar[languagecode]">
<head>
$headinclude
<title>$vboptions[bbtitle] - $vbphrase[addonchat_nav_link_title]</title>
</head>
<body>
<center>
<applet code="Client.class" codebase="http://$addonchat[server_name]/current/" archive="scclient_$addonchat[language].zip" width="100%" height="100%" alt="AddonChat Chat Software" MAYSCRIPT>
<param name="room" value="$addonchat[account_id]">
<param name="autologin" value="$addonchat[enable_auto_login]">
<param name="username" value="$addonchat[username]">
<param name="password" value="$addonchat[password]">
<param name="url.exit.enable" value="yes">
<param name="url.exit" value="$addonchat[exit_url]">
<param name="iconsize" value="0">
<param name="timestamp" value="yes">
<param name="audio" value="yes">
This forum uses <a href="http://www.addonchat.com/">AddonChat Chat Software</a>.<br /> <br />
To use this chat room, you will need to <a href="http://www.java.com/">Download Java</a>.
</applet>
</center>
</body>
</html>
WM3 does not recognize height and width set as percentages, and this make Firefox work abnormally. Those values need to be changed as required like below:
width="1024" height="768"