Firefox tabs are a great way to organise your surfing habits no matter how many sites or pages you want to visit at one time.
However, you can only view one page at a time and it's very easy to lose track of what you've got open and for how long for. Aging Tabs allows you to see how expired your tabs are because they change colour according to how old they are. You can define what colour you want them to change to and over which time period with Aging Tabs.
Aging Tabs also gives new colour to tabs that have just been opened or have been reopened after recently closing them. At the end of the day, Aging Tabs is not a major innovation but it does allow you to keep much better tabs on what you've got open and for how long for. However, whether you really need to do this or not is the big question - maybe it's a good way to stop Firefox hogging so much RAM by reminding you to close tabs.
Aging Tabs is an easy way to add an extra touch of organisation to Firefox and make sure that you know exactly how long tabs have been open for - should you ever need to know.