Ok, this issue confused me at first, but I think I figured it out. I was surprised that you could not do anything in the "attachments" or "downloads" section of preferences, because I have made this change to Thunderbird in Linux in the past. So I downloaded Thunderbird to my Windows machine at work (I had some free time today) and tried the suggestion I gave you, with the same lack of success that you described. However, I nosed my way around the user settings files and found the solution (for me anyway):
In /home/username/.thunderbird (or C:\Documents and Settings\username\Application Data\Thunderbird in Windows) there should be a profiles directory. Enter that directory and the sub-directory for your profile (I only have one). There is a file called mimeTypes.rdf. This is where the file association info is stored. To associate Firefox with HTML attachments and links, you need to add some code:
You should find an element like this:
Code:
<RDF:Seq RDF:about="urn:mimetypes:root">
</RDF:Seq>
Insert the following line between those two tags:
Code:
<RDF:li RDF:resource="urn:mimetype:text/html"/>
After the </RDF:Seq> tag, but before the </RDF:RDF> tag, add the following:
Code:
<RDF:Description RDF:about="urn:mimetype:text/html"
NC:value="application/html"
NC:fileExtensions="html"
NC:description="HTML Document">
<NC:handlerProp RDF:resource="urn:mimetype:handler:text/html"/>
</RDF:Description>
<RDF:Description RDF:about="urn:mimetype:externalApplication:application/html"
NC:path="C:\Program Files\Mozilla Firefox\firefox.exe"
NC:prettyName="firefox.exe" />
<RDF:Description RDF:about="urn:mimetypes">
<NC:MIME-types RDF:resource="urn:mimetypes:root"/>
</RDF:Description>
<RDF:Description RDF:about="urn:mimetype:handler:text/html"
NC:saveToDisk="false"
NC:useSystemDefault="false" />
Note: the path above is for my Windows machine, adjust it to the path for Firefox on your computer.
If the only mimetype you are associating is HTML, your complete mimeTypes.rdf file should look like this (with your path in place of mine, of course):
Code:
<?xml version="1.0"?>
<RDF:RDF xmlns:NC="http://home.netscape.com/NC-rdf#"
xmlns:RDF="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<RDF:Seq RDF:about="urn:mimetypes:root">
<RDF:li RDF:resource="urn:mimetype:text/html"/>
</RDF:Seq>
<RDF:Description RDF:about="urn:mimetype:text/html"
NC:value="application/html"
NC:fileExtensions="html"
NC:description="HTML Document">
<NC:handlerProp RDF:resource="urn:mimetype:handler:text/html"/>
</RDF:Description>
<RDF:Description RDF:about="urn:mimetype:externalApplication:application/html"
NC:path="C:\Program Files\Mozilla Firefox\firefox.exe"
NC:prettyName="firefox.exe" />
<RDF:Description RDF:about="urn:mimetypes">
<NC:MIME-types RDF:resource="urn:mimetypes:root"/>
</RDF:Description>
<RDF:Description RDF:about="urn:mimetype:handler:text/html"
NC:saveToDisk="false"
NC:useSystemDefault="false" />
</RDF:RDF>
Hope that works for you. Happy Thunderbirding!