To install Mozilla Firefox Extensions, you can install from the web or drag the .xpi file into the browser extension window.
Its name implies, download Statusbar is an active status bar that lets you keep an eye on all your downloads in Mozilla Firefox.
You've probably seen, by default Firefox is a small window where you can view the file downloading process from the Internet. However, this window is external and you can not see it using the browser.
No more problems with Download Statusbar, because you will see every download in Firefox on the browser's status bar.
If it is not used, the status bar is hidden and you can pause, resume or open the files you download with a click of the mouse. Plus, download Statusbar opens your browser and then downloads the information in their continuous queue and lets you add an external antivirus that you can use to scan files before using it.