Whitespace is the use of compound words in file and folder names. For example, the link, "href="my usefull sites.php", uses whitespace which many browsers will consider a malformed link. You have spaces between the words "my usefull sites.php". That IS NOT a link. Better to shorten it to sites.php, but if it helps you to remember what it is by file name then...
href="my_usefull_sites.php" or href="my-usefull-sites.php" or href="myusefullsites.php" will work in the link tags.
Right now with the asking for password, you may have your pages CHMOD to the wrong value. 744 is the usual CHMOD value unless the PHP setup says otherwise for a file.
For FileZilla dropout may occur because of this:
The TCP specifications do not set a limit on the amount of time a connection can stay idle. Unless explicitly closed a connection is assumed to remain alive indefinitely. Many routers and firewalls however automatically close idle connections after a while. Worse, they most of the time don't even notify the endpoints of this, instead they just silently drop the connection. So for FTP this means that during a long transfer the control connection can get dropped, but neither client nor server get to know about it. So when all data has been transferred, the server still thinks the control connection is alive and sends the transfer confirmation reply over the control connection. Likewise, the client as well thinks the control connection is alive and waits for the reply from the server. But since the control connection got silently dropped, this reply never arrives, eventually causing a timeout.
In an attempt to solve this problem, the TCP specifications include a way to send keep-alive packets on otherwise idle TCP connections, to tell all involved parties that the connection is still alive and needed. However, the TCP specifications also make it very clear that these keep-alive packets should not be sent more often than once every two hours. Thus, with added tolerance for network latency, connections can stay idle for up to 2 hours and 4 minutes.
The problem is that many routers and firewalls drop connections that have been idle for less than 2 hours and 4 minutes. Such behavior is violating the TCP specifications, RFC 5382 makes this very clear. In other words, all routers and firewalls that are dropping idle connections too early are broken, they just cannot be used for long FTP transfers. Unfortunately manufacturers of consumer-grade router and firewall vendors do not care about specifications, all they care about is getting your money and thus only deliver barely working lowest quality junk.
To solve this problem you need to uninstall affected firewalls and replace the faulty routers with a quality one.
Switching from one mode to the other may help. Some FTPs have a way to send a keep alive to prevent server closing.