I experimented with Prism before under Windows, and have recently resurrected it under Ubuntu Linux 12.04 LTS, using XFCE4 as my desktop.
One of the things I've been playing with is TiddlyWiki, a personal notebook. TiddlyWiki is implemented in HTML, CSS, and JavaScript, and is contained in a single file. The problem is, recent changes in the browser security model have broken it, by placing restrictions on what might be done with things opened from file:// URLs. Under current versions of Chrome, Firefox (my preferred browser), and Midori, Tiddly complains it is unable to save changes, and requires a Java applet as a plugin helper to do the saves. (Oddly, under current SeaMonkey, it works: the browser pops up a dialog box about possible unsafe access and asks for permission, but once given, it works as expected.)
Because I don't need tabs for the usage, and don't need the overhead of a full browser, Prism looked like an appropriate solution, since the version of Gecko it implements dates from before the security model changes. I grabbed the last 0.9 version as a tar.gz file, and extracted it to /opt/Prism. I put the empty.html file that you get in a TiddlyWiki download, and put that in /opt/TiddlyWiki. I then ran prism from the /opt/Prism directory. It loaded, and pit up a dialog box asking for configuration. I pointed it at the TiddlyWiki empty.html file. It created an icon on my desktop. Double-clicking the icon brought up TiddlyWiki in a Prism window, and everything works as expected.
I'm not sure why Tracy had the issue installing under Linux Mint. Things Just Worked here under Ubuntu. The parsing error looks like an issue I've seen with the odd broken Firefox extension. As a matter of eliminating variables, I installed Prism in its own directory carefully separated from extant Mozilla stuff (since I have Firefox, SeaMonkey, and Thunderbird installed, and both release and beta versions of Firefox.
Alas, the Firefox add-on isn't a replacement. What it does is generate a config file for the website you point it at which can be used with Prism. It's a convenience, but it's easy enough to generate the resulting .webapp file manually.