You can set browser.tabs.tabmanager.enabled = false on the about:config page to hide the "List all tabs" (Tab Manager) button.

You can open the about:config page via the location/address bar. On the warning page, you can click "Accept the Risk and Continue"to open about:config.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Firefox 106+ has a "Firefox View" button at the left end of the Tab bar that you can remove via "Remove from Tab Bar" via the right-click context menu.

• https://support.mozilla.org/en-US/kb/how-set-tab-pickup-firefox-view

Thanks for the quick help! I have set browser.tabs.tabmanager.enabled = false, and indeed the dropdown button at the right has disappeared. But the + button at the left is still there, so the tab bar still does not disappear. It looks like this

tab:only-of-type, tab:only-of-type + #tabs-newtab-button {

  display: none !important;

}

does no longer work with the current Firefox version. Some change or replacement is needed for this code.

Try this code in userChrome.css with the Firefox View button and the the "List all tabs" (Tab Manager) button hidden/removed.

tab[first-visible-tab=true][last-visible-tab=true],
tab[first-visible-tab=true][last-visible-tab=true] + #tabbrowser-arrowscrollbox-periphery{
  display:none!important;
}
#tabbrowser-tabs, #tabbrowser-arrowscrollbox {min-height: 0 !important;}

This works. Thanks a lot!

I had the same problem with FF106 and cor-el's solution worked for me as well. Many thanks.