Rated 5 out of 5 stars

I really liked this addon, big thanks to the developer!
To (always) show the quota on TB 78+, open the Thunderbird Config Editor (First page in settings, just scroll down or maybe see here https://support.mozilla.org/en-US/kb/config-editor) and search for “mail.quota.mainwindow_threshold.show” and set it to 0.
Now you’ll see your quota when you click on an account on the right side of the status bar.