I choose "No" but next time I started Firefox I got the same message. In Tab Mix Plus options, on Session screen, "Use Firefox's built-in Session Restore feature" is always checked. I clear it, then press Apply - got the message:Firefox has a built-in session restore feature.
Would you like to enable built-in session restore and disable the Tab Mix Plus Session Manager?
I choose "Yes" but the option remains checked.Would you like to enable Tab Mix Plus Session Manager and disable the built-in session restore?
No such troubles if FM Firefox is deployed (customized) stand-alone, without using mozilla.adm.