Rated 5 out of 5 stars

This is a somewhat time-consuming patch, but I've managed to Toolbar Buttons working in TB 60.

Tested on Toolbar Buttons Nightly with Thunderbird 60.7.2 x64 on Windows.

1. Go to the Add-on home page link at right.

2. On the site's toolbar, hover over "Toolbar Buttons" and select "Custom Button Sets".

3. At top of page select locale and applications (OK to select all apps). At bottom of page select preferred settings, icon sizes, update stream. (NOTE: Tested with "Nightly" stream, "Standard" icons, and all options deselected except for "Offer for download instead of installing".)

4. Select all buttons EXCEPT for "Menu". Or, select custom set of what you need, so long as it doesn't contain the lone "Menu" button.

5. Click Download button and save .xpi file.

6. Unzip the .xpi file (change extension to .zip to extract natively, or use 7-Zip or other extractor).

7. In extracted root folder, go to "chrome" folder, then go to "content" subfolder inside of "chrome". Open "messenger-options.xul" file in text editor.

8. Search for line (no end quotes): "<?xml-stylesheet href="chrome://global/skin/global.css" type="text/css"?>"

9. Add new line underneath (no end quotes): "<?xml-stylesheet href="chrome://messenger/skin/preferences/preferences.css" type="text/css"?>"

10. Save file.

11. ZIP up addon, keeping complete folder structure. Change .zip extension to .xpi.

12. Install in TB 60.

-- Icons do not seem to appear for any of the addon's buttons in the Customize Toolbar window, but they do appear correctly when moved to toolbars. (Easy linking fix in the code???)

-- Depending on system or other addons that touch icons (e.g. CustomizeMyBird), possible visual/sizing glitches on the toolbars (looks pretty good on my own system).

-- Some isolated individual buttons may not work anymore due to changes in TB code, but vast majority work fine. (e.g. "about:about" now asks for an outside browser to view pages; "Add-on Preferences" now seems to be mostly non-functional due to code changes for new "Tools" menu "Add-on Options" item.)

-- Edits to "messenger-options.xul" fixes the Options window to work correctly in TB 60. Otherwise the Options will freeze all other Thunderbird tabs and settings won't stick. Including the "Menu" button in the pack causes all toolbar buttons from the addon to vanish and leaves the Options tabs unpopulated.

-- Unclear why the lone "Menu" button in the pack is the one causing so much trouble. A fix for that button's code would make the complete addon d/l work with the above edits, but without the need to do the time-consuming clicking on the "Custom Button Sets" site.
Those using Waterfox 56 or Basilisk who want full browser support can make the following additional edits. . .

1. Do all of above in Part I, making sure to OMIT the "Menu" button from the custom set.

2. Do #6 in Part II, then open "install.rdf" from the root folder in a text editor.

3. Search for the line (no end quotes): "<!-- Pale Moon -->". Copy the entire associated "targetapplication" string to a new set of lines.

4. Make the 2 following changes to that copied string: (1) "em:maxVersion" to "*" (no quotes around asterisk. (2) "em:id" to "{ec8030f7-c20a-464f-9b0e-13a3a9e97384}" (no quotes).

5. Save file.

6. Open "chrome.manifest" from the root folder in a text editor.

7. Search for the string "/content/browser-options.xul" (no quotes) on a line that starts with "override". Copy that ENTIRE LINE to the next line. (NOTE: the alphanumeric string that appears after "chrome://toolbar-button-" throughout the file is a unique ID populated by the Custom Button Sets maker. Make sure you do not change this, and that all such ID's in the file match.)

8. On the copied line, search for "application=" (no quotes) and change the GUID to "{ec8030f7-c20a-464f-9b0e-13a3a9e97384}" (no quotes). (This edit is what makes the addon compatible with FF56-derived, non-Pale Moon browsers again.)

9. Save file.

10 (OPTIONAL). Make all other Thunderbird-specific edits in Part II #7-10, or omit if only using addon in a browser.

11. ZIP up addon, keeping complete folder structure. Change .zip extension to .xpi.

12. Install in Waterfox, Basilisk, Thunderbird, Pale Moon, SeaMonkey, etc.