Lubuntu 21.10, Desktop: LXQt
Current Thunderbird snap (91.3.1) exceeds 100% CPU usage when Preferences tab is open, causing entire system to hang. Do not know what’s happening, but a screenshot (taken with mobile phone) of the top window is attached. Have to either kill the job manually or right-click the item in the panel and end process.
EDIT: It appears that it was the English-US Language Pack causing this, once I was able to remove it, Thunderbird’s behavior was normal again.