WHere'S the button? Rated 4 out of 5 stars
1. A BUTTON. Odd that there's no button for that one, it would be so useful... It should be simple enough to implement, I use AllInOne sidebar and I would add the button to its toolbar. If you clicked on it, it would open your currently selected tab into the panel. And if the panel is closed, it would either solely open it (with its previous content or blank page), either load the current tab into it, depending on some configuration option.
2. The possibility to have the panel vertical on right or left, or horizontal on top or bottom.
3. Since we can't open more than one panel, tabs should be allowed. I wonder if it would be possible to "embed" a new chrome container for an iFrame or WebPage into the panel...
4. An option menu, for specifying: when pressing the button panel, either automatically open the current page into the panel, either open the panel showing the previous content - if the button is clicked when the panel is already opened, the choice to do a close panel command or to refresh its content with the current selected tab; The location of the panel (top, bottom, left, right).