This is the list I am starting of good Firefox extensions. Each of these is one I would highly recommend.
1. Download Statusbar
This extension will show downloads in a bar at the bottom of the window. The bar is present within all tabs. Items can be opened or cleared by right clicking on the bar.
2. Down them All
This is a good downloader program for quickly downloading files. It can resume incomplete downloads and initiate multiple connections to speed up downloading. There are 2 modes when downloading. One mode allows you to select the destination for the download and the other starts the download using the last saved location. This makes it easy to start many downloads to the same location without extra effort.
3. IE Tab
This extension opens IE (Internet Explorer) only pages in an “embedded IE” tab. It does not have the full functionality of IE pages but it can be useful in some situations. I still find that I need to have IE on the machine for some tasks.
4. Duplicate Tab
This allows you to duplicate a tab so that you can keep your current location with its history and continue browsing using the same history in a different tab. It is similar to opening a new Window in IE but within a tab instead for easier browsing.