From MozillaZine Knowledge Base

Symptoms

In Windows, when trying to save an e-mail attachment, Thunderbird appears to hang for 10-45 seconds. It may appear that Thunderbird won't recover, but if you wait long enough, you are presented with a dialog box that lets you choose where to save the file (or the file is saved, if your Thunderbird preferences are set to always save to a specific location.)

Solution

This can be caused by a bloated "downloads.rdf" file in your Thunderbird profile folder. Try the following.

1. Exit Thunderbird if it is running.
2. Recommended: make a temporary backup of your Thunderbird profile folder (or at least of the downloads.rdf file).
3. Delete the downloads.rdf file from your profile folder.

External links

• Bug 239136: Thunderbird needs to integrate with the new download manager (fixed as of 2006-02-01 trunk builds)
• Bug 320744: no way to clear downloads.rdf (fixed as part of Bug 239136)
• Forum article dealing with this issue