Bugzilla

It would be useful to have one Unified toolbar which is fully customisable. 

I like the idea of  "We're considering an option to show the Menu Bar inside the Unified Toolbar"
Just add two or more lines to the Unified toolbar and put the 'Menu Bar section at the top starting on the left. 
It is going to be necessary to allow users to create new lines in the Unified toobar, so anything they add can be set up in an uncluttered logical manner for the User.

Ideally, I would move the 'Menu icon' onto the 'Menu bar' and place to the left of 'File' as it is part of the menu group and I would have expected it to be in menu location.

Currently I've also had to move the 'Write, Tag ' onto Menu bar,  I tried adding the 'Get Messages' but it remains greyed out, so unuseable.  Adding anything to the Menu Bar is not ideal as you have mentioned.
I've also had to add the Addons & Thremes to Menu bar, but this is not really correct at all because Addons and Themes would be better in the left 'Spaces Toolbar'. 
Could 'Addons and themes' be added to the 'Spaces toolbar'?

In Folder Pane header  - I removed the blue button
The pretend Blue button is unecessary, highly distracting and illogical and composing emails has nothing to do with the Folder Pane. The + sign has nothing to do with writing, it's already generically used in thunderbird to mean add a line. 
Hence adding  'Write' with pen icon for writing an email onto the Menu Bar toolbar. 

But if there were several lines in a Unified toolbar then I could have all menu at the top and items like Write below it and everything would be tickety boo. 

Now that's what I call a design which offers Users the flexibility to create the right working environment to suit their needs.

So yes, a single fully customizable Unified toolbar with Menu bar set at the top and the ability to add lines, so preventing everything trying to get squeezed into one line gets my vote.

It would be useful to have one Unified toolbar which is fully customisable. 

I like the idea of  "We're considering an option to show the Menu Bar inside the Unified Toolbar"
Just add two or more lines to the Unified toolbar and put the 'Menu Bar section at the top starting on the left. 
It is going to be necessary to allow users to create new lines in the Unified toobar, so anything they add can be set up in an uncluttered logical manner for the User.

Ideally, I would move the 'Menu icon' onto the 'Menu bar' and place to the left of 'File' as it is part of the menu group and I would have expected it to be in menu location.

Currently I've also had to move the 'Write, Tag ' onto Menu bar,  I tried adding the 'Get Messages' but it remains greyed out, so unuseable.  Adding anything to the Menu Bar is not ideal as you have mentioned.
I've also had to add the Addons & Thremes to Menu bar, but this is not really correct at all because Addons and Themes would be better in the left 'Spaces Toolbar'. 
Could 'Addons and themes' be added to the 'Spaces toolbar'?

In Folder Pane header  - I removed the blue button
The pretend Blue button is unecessary, highly distracting and illogical and composing emails has nothing to do with the Folder Pane. The + sign has nothing to do with writing, it's already generically used in thunderbird to mean add a line. 
Hence adding  'Write' with pen icon for writing an email onto the Menu Bar toolbar. 

But if there were several lines in a Unified toolbar then I could have all menu at the top and items like Write below it and everything would be tickety boo. 

Now that's what I call a design which offers Users the flexibility to create the right working environment to suit their needs.

So yes, a single fully customizable Unified toolbar containing the Menu bar set at the top and the ability to add lines, so preventing everything trying to get squeezed into one line gets my vote.