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

status_bar_functionality

1.Add-ons icons

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>

extension icon on Add-on Bar in Firefox 4

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.

link URL preview in Firefox 4 address bar

#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)