I'm not sure if the Devs are working on a new one, but you could try to just install the current one. This is not guaranteed to work as Firefox has made a few significant changes between 3.5 and 3.6 but I think its worth a shot. You will only need to do a minor modification as follows.

Download the current .xpi. The .xpi files are just a .zip file with a different file extension. So open the .xpi with an archive tool (you may need to change the file extension to .zip) and extract the files. Open the install.rdf with a plain text editor. Look for a section in the code that resembles this:

<!-- FireFox -->
    <em:targetApplication>
        <Description>
        <em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
        <em:minVersion>3.0.12</em:minVersion>
        <em:maxVersion>3.7a1pre</em:maxVersion>
        </Description>
    </em:targetApplication>

It will not look exactly like this as I took it from another extension (Adblock Plus). It should be fairly self explanatory. As you may be able to see the Adblock Plus extension will install on any version of Firefox from 3.0.12 (minVersion) through to 3.7a1pre (maxVersion). Basically you need to change the maxVersion value (it will probably be 3.5.* or similar in TKL Torrent addon). I suggest just changing it to 3.6.* (yes you can use an asterisk (*).

Once you have edited install.rdf then repackage the extension as a zip file and change the extension from .zip back to .xpi. Then install. You can either just drag and drop it into Firfox, or in Firefox, File>>Open File>>browse to .xpi you created.

Good luck and I'm sure the community would be pleased to hear how you (or anyone else) go with that and if it does indeed work.

 If it does work, prehaps you could attach your modified .xpi so others can use it.

Perhaps Firefox 3.6 has broken something important with the torrent handler?! Maybe thats whats causing this problem...?

If you think its MLDonkey, then perhaps have a look/post over on their forums.

Any update on this? I am still unable to download anything because of the "Parsing URL".

Not sure why but it is working again for me. Pretty weird that it works randomly - I havent changed anything.

Looks like it stopped working again. Now when I try to download a torrent using the FireFox plugin I get an error saying the connection has been reset while the page was loading.

I get the same error when I go to the advanced section of the web interface where I monitor the downloads.

I really wish I could get this thing working in a stable environment.

Ever since my downloads stopped this afternoon, when I click on on Basic I get taken to a "Clutch Web Interface" whereas before I got taken to "Plex GUI" -- which is it supposed to be?

You'll need some input for the TKL Devs (Alon and Liraz) to troubleshoot this problem. Or perhaps MLDonkey if you think that's the problem.

I installed on a new VM from the ISO and was able to start downloading 2 torrents. All of a sudden, the same thing! In the middle of downloading my torrents I got the error!

My next step is to try on a physical machine before giving up.