From the add0n page "[2] How does multi-threading work" (it doesn't by default in Firefox):
> Note to the Firefox users: at the time of writing this documentation, Firefox browser still does not support "FileSystem" APIs that are required to handle file creation and segmented writing. This extension has a wrapper module to use "IndexedDB" APIs but this method is not efficient so it is disabled. As soon as the "FileSystem" APIs get supported by Firefox, the extension automatically uses them and multi-threading will work.
From the add0n page "[2] How does multi-threading work" (it doesn't by default in Firefox):
> Note to the Firefox users: at the time of writing this documentation, Firefox browser still does not support "FileSystem" APIs that are required to handle file creation and segmented writing. This extension has a wrapper module to use "IndexedDB" APIs but this method is not efficient so it is disabled. As soon as the "FileSystem" APIs get supported by Firefox, the extension automatically uses them and multi-threading will work.