I've tried many vertical tabs add-ons for Firefox, but, sadly, none are at the point where I can use them consistently. Some issues that I had:
- interface buttons disappeared: new tab, tab groups
- bugs when reordering tabs
- looked out of place/ugly even with the default theme
That said, this is a sufficient hindrance for me daily that I'm considering learning add-on development to be able to fix these issues in those add-ons or create my own.
One thing that I'd love to have is the ability to reverse the order of the tabs and place the buttons at the top of the vertical tab bar instead of the bottom. I'm surprised that it isn't an option in any of the ones I tried: having the new tab button near the menu button would be a big usability improvement for me (I use the vertical tab bar on the right).
I've been using it for, I think, 2-3 years. And it's come a long way since the early days when it was buggy. I suggest you give it another go with a more recent version. And don't be put off by the ugly screenshots on the add on page as it's not quite what it looks like anymore.
One thing that I'd love to have is the ability to reverse the order of the tabs and place the buttons at the top of the vertical tab bar instead of the bottom. I'm surprised that it isn't an option in any of the ones I tried: having the new tab button near the menu button would be a big usability improvement for me (I use the vertical tab bar on the right).