tbhints is a Thunderbird extension that allows opening links within messages from the keyboard similarly to browser extensions like Pentadactyl, Vimperator, VimFX, Tridactyl, Vimium, LinkHints, etc.
tbhints can be installed by zipping the contents of the src/ directory into a file (or running make tbhints to produce a xpi file in the build/ directory) and installing it via the Thunderbird addons manager.
It can also be installed temporarily from the Tools->Developer Tools->Debug Addons page by selecting the manifest.json file in the src/ directory.
From the main folder tab (with the message preview pane not hidden) or a message tab, press ctrl+shift+E to activate link hinting.
If the message contains links, boxes with one or two letters should appear over the links and a text box should be focused at the bottom of the message.
Enter one of the strings of letters to open the link with the default web browser.
Hitting Escape with the input box focused or entering an invalid hint string in the input box will hide the hints and the input box.
The MailExtensions API limits command bindings to modifier plus key.
To trigger hints from a single key (or a different combination of keys), the tbkeys or tbkeys-lite extensions (version 2.2 or newer) may be used.
To do so, the command should be "memsg:tbhints@addons.thunderbird.net:show-hints".
tbhints uses an Experiment to focus the hint selection input box on the folder tab.
Experiments require full access to Thunderbird and present a warning about this at extension installation time.
It would be great to find a convenient way to capture hint input without needing an Experiment.
Hints can be triggered from another MailExtension by using browser.runtime.sendMessage() to send a message with content "show-hints" to tbhints.