From MozillaZine Knowledge Base
In Firefox (version 2.x and below) and Mozilla Suite/SeaMonkey, downloads.rdf is the (only) place that stores information (such as file name, URL, and date of download) about files downloaded. Its contents can be viewed and managed through the Download Manager and its associated settings. In Thunderbird, it is the (only) place that maintains a history of attachments opened or saved by double-clicking on files listed in the Attachments pane or by using the menu sequence "File -> Attachments -> [attachment name] -> Open". Thunderbird has no user interface for viewing or managing the contents.
Note: Starting in Firefox 3.0, download history is stored in downloads.sqlite instead of downloads.rdf.
It's not advisable to edit this file manually because of its complexity and the fact that, in Firefox and Mozilla Suite, the Download Manager provides an interface to edit it.
This file can be moved to a different profile without any extra effort.
Deleting downloads.rdf will clear your download history. A new file will be created on start up or when the application first needs to write to the file.
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