Recently have been using Free Download Manager with good results. Thing is, the most recent version, 5.x, is complained about as bloatware with decreased functionality. Advice which I took was to install the last good version, 3.9.7 build 1627 available at Filehippo. Integrates as seamlessly with FF plugin Flashgot as NetXfer did.
DownloadThemAll! worked great but this works a little better.
For years I have always used the highly customisable GetRight
downloader (triggered in Firefox via Flashgot
integration). GR still is a superb downloader - very aggressive and persistent, can searche mirrors, etc. - and its unique (?) "download site browser" capability can come in very
handy on shy/reluctant sites.
However, I don't really need to use GR in Slimjet
(wot I have now migrated to), as Slimject has a built-in downloader and the option to use "turbocharged download manager"
as the default downloader (can be bypassed temporarily by holding down the ALT key). The TDM
seems to be at least as aggressive/persistent as GetRight. You can also set the default maximum number of connections used by TDM (which can be very effective in helping to speed-up downloads and make optimum use of available bandwidth), though TDM does not have the equivalent flexibility of GetRight - e.g., to search mirror sites, etc..