Firefox shortcut for opening a new tab near to the current tab

Firefox has a built-in setting (about:config item browser.tabs.insertRelatedAfterCurrent) to automatically open tabs next to the current tab, but it only works when clicking a link inside the current tab, and will then open that tab next to the current one. But if you click the New button or press Ctrl+T, it will always add the new tab at the end of all the tabs.

To change the the way that New-Tab works, install the add-on Open Tabs Next to Current.

A non-add-on way is to use the bookmarklet described here:

javascript:window.open('about:blank');void(0);

Click the bookmarklet in the Bookmarks Toolbar or assign it a keyword to open a new tab after the current one.