Test:
- Take a clean Moodle or rename your config.old
- Run moodle (Installation script)
- Go through the installation to the "Server Checks" page.
- No icon image ( Firefox) or missing images (IE).

Cause:
weblib.php:
doc_link(...) {
...
if (empty($iconpath)) {
        $iconpath = $CFG->httpswwwroot . '/pix/docs.gif'; // PROBLEM: $CFG->httpswwwroot isn't define in install script
    }
...
}

Quick fix:
install.php:
case ENVIRONMENT: /// Environment checks
 + // Set CFG->httpswwwroot default value
 + // it is used to display icon image by doc_link() in weblib
 + global $CFG;
 + $CFG->httpswwwroot=$INSTALL['wwwrootform'];