GoKawiilFix found for Firefox's broken resumable large-file downloads
A user investigating unstable large downloads in Firefox found that the browser's default network.http.response.timeout setting of 300 seconds, present since Firefox 28, interferes with resuming interrupted downloads. Setting that value to 0 (or a very large number) via about:config reportedly makes large downloads both resumable and more stable, though the fix only works if the server itself supports resumable downloads.