It should be available everywhere. Please enter about:config in the address bar and confirm that browser.tabs.groups.enabled = true.

Hi, For soem reason it was set to false, however changing it to true still did not show the down arrow icon on the far right of tab bar, so I experimented changing browser.tabs.inTitlebar from 2 to the default 2, again to no avail. Only switching from vertical to horizontal tabs in the settings made it appear. It does work now and I can save and close group available in the right click menu of the tab group without loosing it.

here are the relevant settings in about:config: browser.tabs.groups.enabled true browser.tabs.groups.smart.enabled false browser.tabs.groups.smart.optin false browser.tabs.groups.smart.userEnabled true browser.tabs.hoverPreview.enabled true browser.tabs.hoverPreview.showThumbnails false browser.tabs.inTitlebar 2

Do you know what the codes 0, 1 and 2 do for browser.tabs.inTitlebar? Should I set it back to zero? Default is 2 which is off. I don't need the title bar. Thanks for your help!

From This question, it looks like:

  0 => Show title bar
  1 => Replace title bar with tab bar
  2 => Use platform default