I have destroyed my Debian Jessie installation and I need to reinstall it. I want to back up my Iceweasel passwords and bookmarks, but I can't start the desktop environment anymore, so I have to do it from the command line. Will it work if I just copy the iceweasel directories and paste them into my new installation? If not, is there another way? I don't want to take any chances, so I'm asking here.
Yes, you can just copy your Firefox/Iceweasel profile over. For Firefox your profiles are in $HOME/.mozilla/firefox, and it's similar for Iceweasel.