How can I prevent Firefox from collapsing one tab tree when I switch to another tree?
Before Firefox version 57, the Tree Style Tabs extension had a switchable option for this exact thing. However, the new integrated Tree Style Tabs does not include this option. I know the setting exists somewhere, as if I manually open a tree without switching to it, I can then switch between two trees with one of them collapsing.
I have not looked into this deeply but are you using this extension?
I see the latest version is:
Version 2.3.0 Last updated 4 days ago (Nov 30, 2017)
and there is a long list of features, so I wonder if that version solves your problem?
Can you please confirm that you are using that version and the problem still exists? Thanks.