From the bug report , which also has a screen shot mock up "This would make it easier to identify the folders of diffrent mail accounts. This would also make sense for the top account nodes."
Sorry you were having trouble, but impossible to make progress without further information from you. There are known solutions for performance on Mac. If are still having trouble, please post in the support forum at https://support.mozilla.org/en-U...
To significantly speed up message deletion, us shift+delete, instead of just delete. This will skip the ability to undo the message deletion.If you still have difficulty, please with speed please file a support request https://support.mozilla.org/en-...
You should find that the current version 140 is very fast. If you still have difficulty, please file a support request https://support.mozilla.org/en-US/questions/new/thunderbird
