Context: I am using i3 and multiple Firefox windows across many workspaces, and have Firefox automatically restore the previous session’s windows and tabs.

Issue: When I quit and restart Firefox, all the windows are dumped on the current workspace and I have to spend a minute sending each of them to where they belong.

There is code in Firefox that attempts to restore each window to the desktop it was closed on, but this code does not work on i3 and specifically disabled.

There are general tools for i3 to restore window configuration, but it’s not easy to identify Firefox windows in order to swallow them to their respective workspaces. In particular, a Firefox window first opens with a generic Mozilla Firefox title, and changes that to the current tab’s title a few milliseconds later. This throws off the i3 swallowing logic.

This script is tailored specifically for Firefox. It maintains a list of currently open Firefox windows and recently closed windows both in memory and in a disk file. When a new window opens and first changes its title, it will be moved to the workspace that title was last seen on.

If the script is started while Firefox is already running, it will skip loading the window configuration file and just rebuild its state from the current window configuration.

The state is kept in $XDG_STATE_HOME/i3firefox.json (or $HOME/.local/state/i3firefox.json if $XDG_STATE_HOME is not set).

apt-get install python3-i3ipc

and arrange for this script to run on i3 startup.