Just upgraded to ff 57, every thing is working great except:
1) ff tab bar not hidden
2) when collapsing a tree it overlaps with the tabs and trees above it. I have to keep all the trees expanded now when using the Metal theme!
---
So for those having the same problem with the metal theme, adding this fixes it:
.tab.collapsed {
margin-top: -24px;
}
.tab {
height: 24px
}