If you don’t know status Bar has been removed and it has been replaced with Add-on Bar in Firefox 4, the most important use of Status bar for me is it shows preview of URL at the bottom when we hover the mouse over a link in a page, Mozilla feels Status bar is less useful and most of status bar functionality is relocated to top of the browser in Firefox 4.
Firefox Status bar functionality
2.Link URL Preview
3.Resize Window Control
4.Current loading tasks
5.Progress bar for page loading
6.Notification that page has finished loading
7.Link to download manager with download summary
#1 For Add-on icons Add-on Bar has been introduced, which is hidden by default much like status bar and can be enabled from Firefox button>options>
So for example I installed Firebug extension in Firefox 4 its icon will be shown on add-on bar (you need to enable Add-on bar first for both add-on bar and extension icon on it to visible).
#2 Link URL Preview has been moved to top and appears grayed after the site’s URL in address bar when you hover your mouse over the link on a page.
#3, #4 have been treated unnecessary on behalf of user.
#5, progress bar for page loading has been moved to the top and attached to the tab that is Loading page title appears on tab while page loads.
#6, Once the page has been loaded progress bar(loading) will be gone that means page was fully loaded.
#7, Currently in the latest nightly build I haven’t seen any download summary when clicked on the downloading item in download manager window. (via)