Show page name in browser

Your title is being set by something in your theme or a plugin attaching to the wp_title filter. You can further filter this value or override it entirely by using the same hook and a different priority that executes later.

// add a filter at priority 999 so it will presumably run last
add_filter( 'wp_title', 'my_wp_title', 999 );
function my_wp_title( $title ){
    // use the post to do things like get_the_title( $post->ID );
    global $post;

    // $title will be the current title if you want to str_replace() or something
    $title = "The new title";

    // return the title
    return $title;
}