Unwelcome change to Thunderbird

[Jim]

Mint18
Thunderbird 68.7.0

I remember seeing an update to Thunderbird awhile ago but never shut 
Thunderbird down until today. When I restarted it the Threads Pane and 
the Folders Pane now look like they are double spaced. So now I get half 
as much information in the same space.

Googling leads to a suggestion to put this in chrome/userChrome.css

#threadTree treechildren::-moz-tree-row {

height: 10pt !important;

}

#folderTree treechildren::-moz-tree-row {

height: 15pt !important;

}

The moz support page says neither one of them exists so you must create 
them. I did that and put them under my default profile. When I restarted 
Thunderbird it was still double spaced. I did make the point size 
smaller with no effect.

Looked in the config file. Found entries for 
mail.threadpane.padding.top_percent 10

There was one for bottom_ percent also. I changed the numbers to 5 and 
then 0 with no effect.

It sure is a pain when they make arbitrary changes to such a noticeable 
part of the UI.

Anyone know how to get rid of the double spacing?

Thanks,  Jim