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The Config Editor is accessed via Preferences > Preferences > Advanced -> General > Config Preferences→Preferences→Advanced→General→Config Editor.

Default web browser

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There's a Mozilla KB page on configuring Thunderbird as a Gmail client, listed in the Reference section below.

IMAP settings

Server Settings ->  Advanced -> Show Only Subscribed Folders

In Config Editor (above):

• mail.imap.auto_unsubscribe_from_noselect_folders  Default and desired value: true
• mail.server.default.check_all_folders_for_new  Default false.  Setting it true avoids the user having to wait for mails to be downloaded on opening folders other than the Inbox – but it may degrade overall performance, especially when Thunderbird is started.  When the IMAP server is local it should be OK.  In case of several IMAP servers, the setting can be made for specific servers using mail.server.server<n>.check_all_folders_for_new

Show Only Subscribed Folders

Account Settings→Server Settings→Advanced→Show Only Subscribed Folders

Subscribing

Depending on the setting of TBC"Show Only Subscribed Folders", folders on the server that Thunderbird is not subscribed to are invisible or shown greyed out.

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Folders are shown in grey italics when they have the \NoSelect flag.  Normally this means they can contain subfolders, but not messages.  A good example is the "[Gmail]" folder on Gmail accounts.

List all folders

The folders' tree structure can be flattened via Advanced Account Settings and setting the IMAP Server Directory to null, then restarting Thunderbird.  TODO: was not able to find this setting in TB 17.0 ESR.

Logging

Sample script to be run in the desktop environment:

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In case of trouble with "too many simultaneous connections" (common with bluelight@auroville.org.in), reduce the "Maximum number of server connections to cache" (TODO: presumably on all clients); the default value is 5.  Account settings > Server Settings > Advanced. 

References

Thunderbird as a Gmail client: http://kb.mozillazine.org/Gmail