Rated 5 out of 5 stars
This extension works with TB 60 and modifications indicated by j917863 but "options" does not work. An other modification has to be made in the internal file options.xul (in chrome/content/). add in line 2 :
<?xml-stylesheet type="text/css" href="chrome://messenger/skin/preferences/preferences.css"?>
as indicated in https://wiki.mozilla.org/Thunderbird/Add-ons_Guide_57 , § "Changes in thunderbird59"
I have also modified chrome.manifest by replacing the line concerning customizeToolbar :
style chrome://global/content/customizeToolbar.xul chrome://slideshow/skin/slideshow.css appversion<59.0a1
style chrome://messenger/content/customizeToolbar.xul chrome://slideshow/skin/slideshow.css appversion>=59.0a1