Multi-Account Container extension "corrupt" upon installation

Hi. I'm running TB 9.5 on Ubuntu 20.04. To further improve my privacy, I'd like to install Multi-Account Containers extension to have cookie (session) isolation between tabs. I've tried installing versions that I verified work in vanilla Firefox. All attempts fail with same error "The add-on downloaded from this site could not be installed because it appears to be corrupt." Screenshot here: https://i.imgur.com/zlCxx2I.png

Trac:
Username: TechyGrue

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