I enabled the title bar and it took the colour of my Windows theme. I enabled the Menu Bar and then moved it up above the Unified Toolbar: See info at this link : https://support.mozilla.org/en-US/questions/1422908

I wanted my Menu Bar to have a complimentary colour to the titlebar. I also wanted the same colour for non selected tabs. In addition, I wanted the selected tab to have same colour as Titlebar and the hover over tab to pick up a line colour of a selected tab.

Now it looks like the image shown below.

As in all my useful question & answers, I provide full instructions, so if you have already created a 'chrome' folder and 'userChrome.css' file then you may only need to copy the code.

This is the code I used. You can modify the colours to be whatever you desire. You may find this link useful for colour selection: https://www.w3schools.com/colors/colors_mixer.asp

Please check in Thunderbird to see if a setting needs switching on.

• Settings > General
• Scroll to bottom and click on 'Config Editor' button
• In search type : legacy
• look for this line: toolkit.legacyUserProfileCustomizations.stylesheets
• If it is set as 'false' :
• click on the far right arrow type icon to toggle from 'false' to say 'TRUE'

Now Do this: In Thunderbird

• Help > Troubleshooting Information
• in 'Application Basics' - Profile Folders - click on 'Open Folder'

A new window opens showing the contents of your profile name folder.

• Exit Thunderbird now. This is important.

I'm going to give the full instructions because I do not know if people already know how to create and use a userChrome.css file.

• In the 'profile name ' folder create a new folder and call it 'chrome'. The spelling is important - note it is all lower case.
• Then open a simple text editor program such as 'Notepad'.
• Copy all the text between the lines below and paste it into 'Notepad'.

@import url("chrome://messenger/content/unifiedtoolbar/unifiedToolbarWebextensions.css");
@namespace html url("http://www.w3.org/1999/xhtml");

/* Position Menu Bar above Unified Toolbar and change colour */
#toolbar-menubar {
order: -1 !important;
background-color: #002633 !important;  /* Color of menu bar             */
color:            white !important;  /* Color of the text - if needed */
}


/* Tabmail Tab */

/*Remove the theme override */
.tabmail-tab .tab-background[selected=true]:-moz-lwtheme {
  background-image: none !important;
}
/*Change selected tab colour to match title bar - seafoam teal is #008083 */
.tab-background[selected=true] {
  background-color:  #008083 !important; 
 background-repeat: repeat-x;
}
/*Change colour of the blue top line on selected tab - */
.tab-line[selected=true] {
  background-color: #002633 !important; 
}
/*not selected tab same as menu bar colour #002633*/
.tab-background:not([selected=true]) {
  background-color:#002633 !important; 
}
/* hover on none selected tab force line to seafoam teal #008083 */
.tabmail-tab:hover .tab-line:not([selected=true]) {
  background-color:  #008083 !important; 
}

• Save the file as 'userChrome.css' - note the spelling of this is important - all lower case except the C.
• Save it in the 'chrome' folder. - see attached image as guide.

Check that file really is called 'userChrome.css' and not 'userChrome.css.txt' - it has to be saved as a Cascading Style Sheet (css) and not a text document. So if you see 'userChrome.css.txt' - no problem - just rename it by removing the .txt - you will get ask are you sure as it may effect things - just say yes because you really do want to do it.

Start Thunderbird

If anyone is interested - I have created other 'how to modify' type of questions: As I create them I'll add them as comments, so people can get a quick access to various options.

Note - I always include the full instructions - so if you have already created the chrome and userchrome.css file, then it's you do not create them again.

• Access profile name folder
• Exit Thunderbird
• click on chrome folder
• open 'userChrome.css' file
• copy the relevant part of code and paste into 'userChrome.css'
• save the file
• start Thunderbird.

Remember - always exit Thunderbird before editing the 'userChrome.css' file.

Supernova 115* How to create zebra alternative row stripes in Message List

• https://support.mozilla.org/en-US/questions/1425551

Supernova 115* How to reduce the spacing in the Message Header area.

• https://support.mozilla.org/en-US/questions/1429674

Supernova 115* - How to increase the minimum height of 'Thread Pane', so you can raise the 'Message Pane' higher.

• https://support.mozilla.org/en-US/questions/1423733

Supernova 115* - How to move the 'Menu Bar' above the 'Unified toolbar':

• https://support.mozilla.org/en-US/questions/1422908