Sorry I didn’t make it more clear, but ALL themes break ColorfulTabs except the Firefox Default theme. There are many thousands of themes that break ColorfulTabs. Clearly the issue is not with any specific theme. Perhaps this issue is with “Classic Theme Restorer” that I have installed?
What is so different about the Firefox “Default” theme that allows ColorfulTabs to work, even when Classic Theme Restorer is enabled — yet every other theme breaks ColorfulTabs?
Thanks again for your time. I know that you are very busy and I really appreciate it.