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'];