These pages are no longer being maintained
I now use SeaMonkey-ppc on my G4

Thunderbird Application Modifications


This page describes a few simple Thunderbird 3.1.x 'improvements' I have made. I do not advise using them on earlier versions. They may be OK on later versions but please observe the following precautions. They are written from a UK POP on PPC Mac perspective but can probably be applied to IMAP and other platforms. Reversing changes and their consequences should not be too difficult as long as profile folders have been backed up before starting. In addition keep a pre-modification copy of individual application files so that changes can be easily reversed.

Message Pane and Quick Filter Bar bug - corrected in version 3.1.3 and later

Versions of Thunderbird 3.1 before 3.1.3 frequently forgot instructions not to display the Message Pane and Quick Filter Bar. This bug affected all platforms and was particularly annoying on Macs.


  1. Control click Thunderbird application and select Show Package Contents
  2. Open Contents/MacOS/modules/sessionStoreManager.js with a text editor
  3. Replace:
    this._currentStateString = null;
  4. Save and test.

Remove Folder Pane unread count

If you want a narrow Folder Pane it helps to remove the unread count after its folders.


  1. Control click Thunderbird application and select Show Package Contents
  2. Open Contents/MacOS/chrome
  3. Open messenger.jar/content/messenger/folderPane.js with Jar Inspector
  4. Find the following consecutive lines with Jar Inspector and disable them by putting ' // ' before the text on each of the 3 lines.
    let unread = this._folder.getNumUnread(false);
    if (unread > 0)
    text += " (" + unread + ")";
  5. Save and test.

Trash folder name:

The Folder Pane's localised Trash folder name can be changed. I prefer 'Trash' to the default British 'Deleted' for my narrow custom Folder Pane. I am not concerned about Deleted and Delete occurring elsewhere.


  1. Control click Thunderbird application and select Show Package Contents
  2. Open Contents/MacOS/chrome
  3. Open en-GB.jar/locale/en-GB/messenger/ with Jar Inspector
  4. Replace:
  5. Save and test.

Sub-folder visibility

I normally have a flat folder structure without sub-folders but I like to see if there are any sub-folders in Trash. This modification defines which folders will show sub-folders when the mail window opens.


  1. Open folderTree.json (in profile directory) with a text editor and ensure that it contains something like the following
  2. The above ensures that any sub-folders in the mail account and its Trash are visible - add or remove items as required
  3. Save
  4. Lock folderTree.json
  5. Test.

Session settings

I prefer to use Thunderbird without the Message Pane or Quick Filter Bar and with Inbox selected when the main window opens. Whilst these settings may normally be remembered this modification ensures that user settings are always used. This change removes the need for the Select Inbox extension. If requirements alter, this modification may need to be reversed by replacing sessionStoreManager.js with an original pre-modification copy and unlocking session.json.


  1. With Thunderbird open adjust Message Pane, Quick Filter Bar and Inbox as required and then quit.
  2. Lock session.json (in profile directory)
  3. Control click Thunderbird application and select Show Package Contents
  4. Open Contents/MacOS/modules/sessionStoreManager.js with a text editor
  5. Find the following line and disable it by putting ' // ' at the beginning of the line
  6. Find the following line
    let data = JSON.stringify(aStateObj);
    insert the following new line before it
    return; // new line added
  7. Save and test.

Yellow Thunderbird Icon

Here is an alternative Thunderbird Icon for OS X.


  1. Download the icon and unzip it
  2. Control-click Thunderbird Application and select 'Show Package Contents'
  3. Go to /Applications/
  4. Rename the original thunderbird.icns
  5. Put the downloaded thunderbird.icns in the folder
  6. Restart Thunderbird
  7. If Thunderbird fails to find the new icon you can paste it into the application's Get Info as usual and drag it to the dock

html | css | 3756 hits since August 2010 | updated 2020-06-07 | webmaster