Web-Based IDE With Firebug & Git Support: Orion
Working completely online is not only a getting popular trend but also something that happens slowly in the background almost without us realizing it.
Many of us have online storage accounts to host our documents/codes, lots of web apps exist to help us accomplish our daily tasks (image editors, cross-browser testing tools, etc.).
It has 2 versions, hosted or self-hosted, and the self-hosted version requires Java to run.
The application supports working with multiple projects, creating files/folders, FTP and there is Firebug + Git integration.
Orion is extensible with its plugin system and it is well-documented.