Buffer mode is very similar to File mode, except that instead of tracking the current directory and all files available there, the current list of Emacs buffers is shown.
These buffers can have their tags expanded in the same way as files, and uses the same unknown file indicator (see File Mode).
Buffer mode does not have file operation bindings, but the following buffer specific key bindings are available:
Kill this buffer. Do not touch its file.
Revert this buffer, reloading from disk.
In addition to Buffer mode, there is also Quick Buffer mode. In fact, Quick Buffers is bound to the b key. The only difference between Buffers and Quick Buffers is that after one operation is performed which affects the attached frame, the display is immediately reverted to the last displayed mode.
Thus, if you are in File mode, and you need quick access to a buffer, press b, click on the buffer you want, and speedbar will revert back to File mode.