When using a vertical tab extension like Vertical Tabs Reloaded, you can hide the tab bar by adding the following line to userChrome.css:
TabsToolbar { visibility: collapse !important; }See multi row tabs for instructions on how to find the userChrome.css file.
This mode may require changing the way new tabs open. Set browser.tabs.insertAfterCurrent and browser.tabs.insertRelatedAfterCurrent (in about:config) according to this table:
insertAfterCurrent | insertRelatedAfterCurrent | |
| open all tabs next to the current tab | true | whatever |
| open all tabs at the end of the tab bar | false | false |
| related tabs next to current, others at the end | false | true |