First of all, YOU CANNOT FIND THIS EXTENSION IN THE ADDONS SEARCH USING THE KEYWORD aging. AWESOME!!!
You should add variable delay aging of tabs. That is, instead of aging each tab statically by a static X seconds, it should in fact age by X seconds the first time, age by Y seconds the next time, and then age by Z seconds the next time it should be aging. Where X < Y < Z
This would age the tab fastest when it matters most (IE: When you are on the computer and browsing around actively), and least when it matters least (When you leave Firefox running overnight and come back). What happens right now is that I come back the next day and find all my tabs are BLACK (Thats the color I use to age) with no indication as to what is newest or oldest. I suppose I can increase my delay in seconds, but I find that my setting works good for short term browsing, but not long term.
Either you should do this, or you should include some kind of exception for idle time (where NO browsing is occuring) where aging happens less and less frequently as idle time increases