-
Arc no longer has its own hide/show shortcut. Hiding is Firefox's sidebar
toggle now — the toolbar button, View → Sidebar, or its shortcut — and the
extensions row hides with it. Arc's own hide mode was stored per window and
survived restarts, so a window could come back hidden with no visible way
out; that state is gone. -
The setup turns on Firefox's Picture-in-Picture on tab switch, so a playing
video pops out when you leave its tab and returns when you come back, the way
Arc does. Firefox has this built in; some profiles ship with it off. -
Dragging a tab above the list drops it at the top. The strip with the divider
and "New Tab · Clear" accepted nothing, so the line stayed on screen while the
drop was refused.
Install: download arc-0.6.0.xpi below and open it in Firefox. Installed copies update themselves.