The purpose of an experiment is to learn something – not neccessarily to make a product. The first phase of the Ubiquity experiment concluded in 2009. It was a success in that by doing it we learned a lot about both the power and the pitfalls of linguistic interfaces for the Web. Jono, one of the main Ubiquity developers, has written a retrospective on lessons learned from the Ubiquity project.
Labs is currently focusing its attention on other experiments. Which is not to say that Ubiquity is over; there will almost certainly be a phase II of the Ubiquity experiment at some point in the indefinite future.
In the meantime, there are still plenty of people who find the Ubiquity extension, experimental as it is, useful enough to keep using it in their daily web activities. Recently, many of these Ubiquity users have been asking for a version of the extension that is compatible with Firefox 3.6, so we’ve decided to do a set of maintenance releases to provide this compatibility.
We’ve already released an update to the 0.1 line, Ubiquity 0.1.9.1, which works with Firefox 3.6. It can be downloaded from Addons.mozilla.com.
The other branch of the codeline, the more experimental Ubiquity 0.5 branch, is turning out to be more difficult to update to Firefox 3.6 than we anticipated. We’re going to have to find some time to do some serious hacking and bug-fixing on it before we can release a compatible 0.5.x version. When we do, we will announce it on this page, so please stay tuned.

Fonte