My fault.   I was connecting to wifi asking for dhcp, of course it will assign dns server and gateway (the port's default route).   Changed the connection type to static  ip, and now it don't mess with the resolv.conf.

Thanks all for the info and advices.

BTW:  I installed wpa_gui and it reports that it "could not get status from wpa_supplicant."   Are the operations of wpa_gui and network manager mutually exclusive?

isn't  that equivalent to "lock" (in synaptic package manger)?

When I wanted to change the setting, looked into files "interfaces" and subdirectory "interfaces.d" in /etc/network, and it was empty, so I was wondering where the configuration settings were stored.    Any way, editing that file and subdirectory seems to do the trick.   Thanks.

BTW, "mismanage" is right.   There are apparently multiple little tools that do not know what the others are doing and things (including myself) get confused.

fsmithred:

You must be the life of party, huh.     Good that you pointed that out, though.  Also, plugins at /usr/lib/mozilla would be shared, and maybe there are more shared resources..

pedro:

Thanks for the info link.

fsmithred:

"Find the older package in /var/cache/apt/archives and install it... "

This particular old package was not in the cache archive.  I am guessing that's because I purged it (instead of uninstalling it) and that also removed the package from the cache as well?

Thanks for the info.  Good to know how to roll back to an older package no longer available at repo.

kapqa:

"to install firefox 52.9 i download it from ftp and then just change the shortlinks in "favored applications" to the firefox directory ..."

I basically did the same - downloaded the older version tar package from mozilla archive.  Are "favored apps" links  the same as "preferred apps" links?

Thanks for the replies.

After resyncing package index, I was able to download firefox-esr 60.9, but I ended up getting the older version (esr 52.9) from mozzila archive.

I suppose there is no way to get the devuan deb package for the older version (esr 52.9) from devuan repos?.