Unfortunately Firefox does not make available the kind of programmatic access required by apps like Tabby. Therefore Firefox windows and tabs are not displayed. 

Not directly. However, it is easy to use your Safari tab groups to try out Tabby without making changes to your tab groups. Simply open a new Safari window and set it to a desired tab group. Repeat that process for each tab group and the next time you open Tabby it will display your tab groups organized by window.

Check to see if you have a Chrome update pending. When Chrome is in that state it refuses connections from Tabby and prevents it from starting up. Complete the Chrome update and Tabby should start up normally.

1. If the browser is not running when opening a Saved window, a second blank window will be opened.
2. Rows in the Saved windows view may appear selected after certain operations. Workaround: mouse over the selected rows.
3. A single minimized Chrome window will not maximize when selected in Tabby. Workaround: keep at least one Chrome window maximized.
4. On certain multiple monitor configurations the Tabby main view may be intermittently displayed partially off-screen. Workaround: re-open Tabby.