If it worked in a prior release then you need to contact the author of the add-on tool you were using, and ask them to update the addon for version 60.

Duplicate of https://support.mozilla.org/en-US/questions/1214835

The Highlighter add-on works here in TB 60b4. To install it, first open Tools/Options/Advanced/General/Config. editor and double-click the preference extensions.strictCompatibility to switch it to false. Then, follow the instructions here to add it to TB.

almost help full .... much appreciated .. however when i get to final step and click "here" i get this: https://support.mozilla.org/en-US/questions/1170298#answer-1006339 and am confused what to do next am i beyond help? thanx again

Right-click the 'Download Now' button on the add-on webpage, Save Link As..., download the xpi file, then in TB, Tools/Add-ons/Extensions click the gear icon next to Search, Install Add-on from File, select the xpi file.

https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

FINALLY !!!!!!!!!!!!!! CAN'T THANK YOU ENOUGH / gk