The API for this is not yet implemented, but you can use a userChrome.css style to do the same thing. Add this to your userChrome.css file:

1. #tabbrowser-tabs { visibility: collapse !important; }

Will this also work to place the tabs underneath rather than above? I was able to do this with previous Firefox but now that's all been changed again. The last time Firefox updated, I stayed away for two years. Hope I don't have to do this again.

If it will work, please explain what you are recommending. I don't understand how to do this:

   userChrome.css file:

   #tabbrowser-tabs { visibility: collapse !important; } 

Can I assume this is for Firefox, even though it says Chrome?

Sorry for my ignorance, but better to admit it than do nothing!

This answer is too complex. There must be a simpler way of removing them. The other answer to "click on firefox button in upper left hand corner then click on options. There are no options on my macbook pro version.

Hi backpackerbill

On Mac you need to open the Preferences instead of Options to make changes to settings, but that won't help with the Tab bar.

Are you using an extension to have the tabs in the sidebar and to you want to hide the regular Tab bar above the Navigation Toolbar?