A few years back, Panorama was a very touted feature of the brand new Firefox 4. It was supposed to be a brand new way of organizing your tabs, making it easier to focus on what you were doing without losing track of tabs you have open but which you don't need at the moment.
That's the theory, in practice nobody used it and few people to this day know what it is, how it works or anything about it at all.
That may or may not be Mozilla's own fault, it added the big new feature but did little to introduce it to users. The point is moot now as Mozilla has decided to remove it from Firefox and offer it as an add-on to the few people that do actually use it.
"Panorama has a very small user base and there's basically no chance that we will enable it by default or even improve its visibility and discoverability anytime soon," Mozilla's Tim Taubert explained in a bug entry on Bugzilla.
"In its current form it is indeed quite fragile and causes intermittent test failures here and there when touching platform code. We're not going to spending any time on improving Panorama and its feature or its design and UX - thus it should just be removed from Firefox," he added.
The good news for those actually using it is that the code will simply be ported to an add-on which will do exactly the same thing.
This way, Firefox becomes lighter since it gets rid of code few people use, and Panorama users can continue to rely on it as they always have.
It will take a while for all of this to happen, but that is the current plan. Mozilla is hoping to make it possible to install this future add-on for existing Panorama users, but there are no guarantees at this point.