1) This ONLY affects Safari. The homepage preference setting in Firefox is impervious to the problem. I don't see any other change in behavior of Safari or of any other Application.
2) Yes, what you describe is what is happening: I launch Safari, and a homepage appears with the address
http://portail.dartybox.com; I go to
http://www.nytimes.com, launch preferences, set that as the home page, and as long as I do not quit Safari or put the Macbook to sleep, the NYTimes remains my home page; when I wake the computer or relaunch Safari, it's back to the dartybox portal as the homepage (and that's what the field reads in Safari's preferences).
3) I tried doing what I suggested above, connecting an Airport Express to the modem/router, and then connecting via Airport to the Airport Express, rather than the ISP's modem, but the problem persists.
In this case, DNS numbers can be added, but one assigned by the modem can't be modified or deleted on either the Airport Express's network settings or my MacBook's, and the greyed-out DNS numbers are the same as the router the device connects to: On the Airport Express, the DNS is the modem's address, and on my MacBook, the DNS is the address of the Airport Express (10.1.1.1). But whatever the modem is doing to alter the home page preference can't be stopped by using the Airport Express as a buffer in the middle.
4) I can't see in the Activity Monitor window anything suspect, but then again the info Activity Monitor generates WAY over my head.
5) I suspect that this is indeed some hard-wired thing in the modem that is simply not negotiable. Google searches in English and French turn up nothing helpful. Nothing at all about this issue appears in English, and only a handful of entries in French from disturbed users come up, but no solutions offered.
6) I don't WANT to use Firefox! I know people swear by it, but I've been a Safari user from Day One and just don't want to give it up over this one annoyance. It's SO ******* me off! >:-/
Edited to add: Sorry about that previous post with the long log lines from Safari's activity window. I can't edit or delete the post, and I know it's made this thread a pain to read...