Sidebar+

WebExtension that imprement Sidebar into browser.

Install from source

Chrome & Opera:

• Open chrome://extensions/
• Check "Developer mode"
• Click "Install unpacked extension" button

Firefox:

• Open about:debugging
• Click "Load Temporary Add-on"

Install from store

Chrome: Removed by Google

Firefox: download

Opera: none yet

Remove tabs

Chrome and Opera no idea

Firefox

• Create "chrome" folder inside your profile folder
• Create file "userChrome.css" inside "chrome" folder
• Copypaste "#TabsToolbar {visibility: collapse;}" info "userChrome.css"
• Restart Firefox

more tricks with "userChrome.css" here