Did you find them by going to the addons entry on the tools menu and searching for them and selecting the install button when they were found.

Or

Are you trying to do it old school where you download a file in a browser and then go to addons on the tools menu and click the cog wheel icon below the search field and select install from a file?

Ref: https://support.mozilla.org/en-US/kb/thunderbird-add-ons-frequently-asked-questions

I selected the Emoji addon from the choices given by Thunderbird. It then says it can't be installed. EDIT: Just got this to install, and the emoji icon appears at the end of the mail toolbar. I used to have a full pane on the right side of my T-bird screen with all the emojis fully visible & selectable at all times. I now cannot see a way to set this up again.