After releasing Firefox 7, Mozilla team has started code migration for other channels. Firefox 8 will land to Beta channel, and Firefox 9 will come to Aurora channel. Firefox 10 has already landed to the nightly channel of Firefox. The most recent nightly build version is Firefox 10.0a1 (alpha).
Firefox 10 Features
The current nightly build is almost similar to the previous Firefox 9 build with just a version number change. Firefox team has a long list of new features for the Firefox 10. Some features currently being considered by Firefox team are: Add-ons default to compatible, plugincheck functionality in add-on manager panel, improved display of location bar results etc. Firefox Mobile may get new features like Text Readability, Flash support (on Android platform) etc.
Along with these possible features, Firefox 10 will bring many new tools for the developers like Console Object Completion, more powerful and integrated Code Editor, Style Inspector and Editor.
(More on Firefox 10)