There are in performing such a task. Changing advanced in the location may cause harm to stability. Do exactly as i say...

Type- about:config -in the address bar and then press enter. Click I'll be careful, I promise! In the filter box type browser.allTabs.previews Double click on the value to set the value to true instead of false. Then close the tab and see the final result

You can use code in userChrome.css to set a lower minimum width for the normal (not pinned APP) tabs to have more tabs visible on the tab bar.
The problem is that Firefox 13+ no longer shows a List All Tabs button unless the scroll buttons are visible, so it can be difficult to locate other tabs. You would need to hover a tab to see the tooltip if you can't see its label.

• chrome://browser/content/browser.css

Add code to userChrome.css below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

The customization files userChrome.css (interface) and userContent.css (websites) are located in the chrome folder in the user profile folder.

• http://kb.mozillazine.org/Editing_configuration

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

/* code used in Custom Tab Width extension */
.tabbrowser-tab[fadein]:not([pinned]) {
 min-width: 100px !important;
 max-width: 250px !important;
}

#tabbrowser-tabs ~ #alltabs-button {
 visibility: visible #important;
}