Alternatively, could you provide the code to toggle it, so I could make a keyboard shortcut myself using Keyconfig add-on.
By the way, I found that clicking on the grippy does not work consistently to show/hide the tab bar. The behavior is like described in #538.
My environment: Windows 7, Firefox 38.0.1, Tree Style Tab 0.15.2015030601.
Actually, if you hold the Ctrl key, while the tab bar is hidden, it is shown.
Don't know if this helps, but looks like the event (aEvent.ctrlKey) is defined here:
content/treestyletab/content-utils-autohide.js
modules/window.js
And actions that use this event are here:
modules/browser.js
modules/base.js
modules/tabbarDNDObserver.js
Showing the tab bar with Ctrl down is different in that it is overlayed on top of content. It is meant to be temporary. I, on the other hand, want to have the bar mostly open, but hide it when the content is too wide.
@piroor why is this out-of-purpose? Many extensions offer keyboard shortcut triggers.
I would like to see this implemented.
This would be a great improvement.
To anyone still looking for this feature, Hide Tabbar extension seems to work.
Now you can toggle TST's sidebar panel with F1 key, on TST 2.0.x.
Is there any way to change which key? I use F1 for my dropdown terminal.
Sadly it is impossible for now. The keyboard shortcut is hard coded here:
and it can't be reassigned dynamically. There are number of bugs around keyboard shortcut and one of them can solve it:
F1 works great for hiding it, thanks for posting that here. It would be helpful if that appeared in the menu bar under View, Sidebar, so I could have discovered it without having to land here. :)
I'm closing this. Thank you for fixing it. And thanks to other commenters for their support.
For anyone else discovering this via Google search: if you're on a Mac, you can do this from the Keyboard prefpane. System Preferences -> Keyboard -> Shortcuts -> App Shortcuts
Screenshot shows Cmd+Shift+3 because I was trying to take a screenshot, but you can set it to anything.

I did the above (Keyboard > App Shortcuts) and it worked ... for a day? Now the same shortcut is sitting there in the menu, but it does not work in Firefox to open/close the tabs on the left side. I even deleted it, redid it the same way, and it still does not work...any ideas?

Most helpful comment
Now you can toggle TST's sidebar panel with F1 key, on TST 2.0.x.