Google Chrome and other Chromium-based browsers: type chrome://extensions in the address bar. Press the thrash can icon next to the Produtools Manuals B2 Toolbar.
Firefox: press Shift+Ctrl+A (or open Tools → Add-ons). Press Disable next to the Produtools Manuals B2 Toolbar. If you can't find the toolbar in the Extensions tab, switch to the Plugins tab and look there.
Opera 12.x and older: press Ctrl+Shift+E (or press the Opera button → Extensions → Manage extensions) to open the Extensions menu. Press Uninstall next to the Produtools Manuals B2 Toolbar.
Internet Explorer: open Tools → Manage Add-ons. Select the Produtools Manuals B2 Toolbar and press Disable.