"when icedragon starts" has no dropdown arrow

It is permanently set to Tab Mix Plus Session Manager and I cannot change it. There is no dropdown arrow such as shows in the Help setup guide.

What opens instead of my home page is the setup screen for Tab Mix. Why would I want the setup each time I open the browser???

I can’t delete it, can’t change it, and I am forced to open my home page by manually opening the bookmark for it as if I didn’t have a home page.