[request] Conditionally switch betwen horizontal/vertical tabs + Containers support

[dhorkin]

I have two monitors set up - one is oriented portrait, the other the more common landscape. When I'm on a landscape monitor, I like using Tree Style Tabs or Sidebery. Paxmod is too cluttered in this configuration. But when I'm on the vertical monitor, the opposite is true - sidebars take up too much room, and paxmod is the best way to use my screen real estate.

When I'm on my Portrait monitor:

• I would like to have normal Paxmod behavior (titlebar disabled)
• automatically close Tree Style Tab or Sidebery if they are open (but leave other sidebars open)
• add some kind of way to display/switch between Sidebery panels (or filter shown tabs by Firefox containers, if Sidebery doesn't have an API, or as fallback)

When I'm on my Landscape monitor:

• I would like to automatically open Tree Style Tab or Sidebery sidebars if they are installed
• either of the following:
  • show titlebar instead of Paxmod tab rows (since they are redundant w/ vertical tabs)
  • replace tab rows with Sideberry "panels" (basically, show what Sidebery shows at the top of their sidebar as the tabs at the top of the screen)
    • Sidebery's panels are by default:
      • "bookmarks" (which is basically embedding the same content as the regular bookmarks sidebar)
      • "default" panel that just shows all tabs
      • you can create additional panels that only show tabs from certain containers
      • you can also largely treat the panels the way you might use windows to avoid unnecessary clutter (i.e. create a new panel and open tabs even if they aren't specialized by container)
    • Note that this request is related: Feature Request: custom rows #82

I will create a related issue on Sideberry and TST in case some of this functionality would require changes on their end.