I had this figured out once, but after a clean install of thunderbird, I need to figure it out again and then record the process here so I will know how to do it the next time.
Not only that, but the Thunderbird nitwits have broken add-ons like Keyconfig.
As of Thunderbird 68.11.0 this no longer works. Apparently the Thunderbird "team" made changes and broke this and other extensions. The author of the Dorando Keyconfig add-on says that he tried hard, but it is now too big of a mess for him to deal with.
Downgrading to Thunderbird 60 is probably the best option at this time.
In thunderbird, use the "hamburger" at the upper right and select "Add ons" from the menu. This brings up an Add on manager" tab, which is a very poorly designed page. Somewhere in the midst of all the hype is buried a "see all" link that gets you what you really want. Type "Dorando" in the search box and it offers you version 2016.2 along with a big button that offers "add to thunderbird". Click this. Then click "install now" in the dialog that ensues. The original description warned you that this requires a restart. There is an easy to miss "restart now" in the upper right.
And this seem to work with 52.1.0 just fine.
Control-Shift-F12 gets you to the control screen to disable keys (or do whatever else you want to do).
Another way is to use the hamburger and then "Add Ons" to get to the lame and stupid add-on manager page, but then go down to "Extensions" and you will see Dorando keyconfig along with the Lightning calendar thing. You can take this opportunity to disable lightning (and I do since I don't use it and I have heard it being implicated with Thunderbird slow downs.). I restart Thunderbird to make this disabling take effect.
Supposedly there is also supposed to be a way to get to the Dorando control screen via the hamburger and then tools, but I sure don't see it.
Adventures in Computing / tom@mmto.org