The goal of this bug is to finalize the design of extensions targets in the Runtime page. This includes: - addon-specific controls (enable addon debugging, install temporary extensions) - regular extensions debug targets - temporary extensions debug targets. They have additional buttons compared to regular extensions: Reload and Remove. They also show an additional field: source location, which points to the temporary extension location on the disk. - error messages for errors that happen when installing a temporary extension - error messages for errors that happen when _reloading_ a temporary extension (note that this is currently not implemented anywhere, reload errors are silently swallowed) - warning messages for regular extensions (eg unsupported property in a manifest) We have a short overview of the current implementation and mockups for extensions at https://docs.google.com/document/d/1KdtKmniLpSuSB8lTwR4mECPeyy8D2mERpjcsrJA_-k8/edit#heading=h.81j48utoy6hm . This UX bug might be split into several more specific bugs if it makes it easier.