LaTeX pagestyle confusion

main.tex

\documentclass[twoside]{article}

\usepackage{fancyhdr}
\usepackage{extramarks}

\setlength{\headheight}{14pt}

\fancypagestyle{ttlpage}{
    \fancyhf{}
    \fancyhead[L]{First page head}
}

\fancypagestyle{simple}{
    \fancyhf{}
    \fancyhead[LE, RO]{\thepage}
}

\fancypagestyle{main}{
    \fancyhf{}
    \fancyhead[LE, RO]{\thepage}
    \fancyhead[LO]{\firstleftmark}
    \fancyhead[RE]{\lastrightmark}   
}

\begin{document}

\thispagestyle{ttlpage} % Causes problems.
%\pagestyle{ttlpage} % Works fine.
first page
\newpage

\pagestyle{empty} % With \thispagestyle above, causes missing \firstleftmark and \lastrightmark
%\pagestyle{simple} % With \thispagestyle above, causes "CONTENTS" to be printed instead of "INTRODUCTION",
\tableofcontents
\newpage

\pagestyle{main}
\section{Introduction}
\subsection{Foo}

\end{document}