kompozer --version
kompozer.net KompoZer 0.8b3, Copyright (c) 2006-2009 contributors
Linux my-laptop 4.18.14-arch1-1-ARCH #1 SMP PREEMPT Sat Oct 13 13:42:37 UTC 2018 x86_64 GNU/Linux
There seeems to be no way to open a web site from the GUI. See screen capture picture. Running kompozer http://website.com in terminal works.
I have the same issue. No "tree" is displayed in Site Manager.
KompoZer 0.8b3 (20100301)
Windows 10 HP15
Work-around:
Using FileZilla (for example) copy the url (ftp address) and paste into KompoZer (File>Open Web Location) dialogue box.