Its a great web browser i have seen so far, there is no doubt about it. But from FF 1.5 onwards, i see very little is done in terms of new "simple" features addition.
By "Simple" features i mean, there should some simple ways of doing routine things anybody would do in their whole day.
For example, i have just tested Opera browser and found few things which are very common for all type of internet user. I saw they have added a "Paste and Go" option in title bar, its just a question of pasting the url in address bar and then clicking on return(enter) or Go button. But it feels very good when it saves you from having that extra click or press of button move. Also they have a niche feature that allows you to select any text in page and add it to Notes by a right click and "Copy to Note". Then you can use that note to paste it in other text boxes on different sites. Very useful for bloggers i feel.
Another thing i found is with IE & Opera both. They have better Zooming feature or i would say different Zooming feature than FF. They zoom the entire page along with images and everything which keeps the page layout same through out the min. zoom to max zoom. But FF does the Zoom very differently. It only zooms the text and when you zoom the page to higher value it entirely breaks the layout of the original page.
I am not sure if these are bigger things from coding point of view, but definitely it improves user experience with a great value.
There are lots of things in FF that so good and are not available in any other browser but if they can add a such smaller and simple things to it, they will get a great amount of applaud from users round the world.
Don't take me wrong, i am not from any other browser camp .. but just trying to show some few simple things which would make the browsing experience a lot better and full of fun for every type of user.
So my suggestion to the FF team is to keep doing great things as they have done in past and now doing, but also take care of such smaller things that helps the user a lot.