I am on linux ubuntu 12.04 LTS. I had two problems, one remaining.
1. Simple click, on globs.org site, to download exteditor-v100.xpi has the effect to show the content of the file in the current firefox window. With saveas button, this is a php file which is saved and not the expected one. I solved this by a direct wget command.
2. I try to "Drag and Drop the new icon External Editor on your toolbar" but what is this icon ?
I tried to install first xpi file as an add-on to TB but there is no "install" button in my thunderbird version (v15), in tools menu entries, which lets you indicate where the addon file is. I know rather well TB but not latest versions.
So I am stuck there. I would be grateful for some help, since I am very frustrated to be stuck at a so early stage. Understanding what occurs for problem 1 would be also of interest.