how to turn off "100 thank yous" start page tab

You can check that those pages aren't set as your homepage(s).

You can check the homepage setting in "Settings -> Home".

• https://support.mozilla.org/en-US/kb/how-to-set-the-home-page

Firefox supports multiple homepages separated by '|' (pipe) symbols.

nope.... I had already tried both ideas, did them again for fun today still have thank you page. comes up 1st thing after launch, I clear it with blue button "start browsing" and then homepage opens (Bing). maybe uninstall/reinstall?