Not allowing the user to accidentally open a duplicate page in a new tab is a feature in Firefox. Copy and paste is the only way that I am aware of, without using an extension.

https://addons.mozilla.org/en-US/firefox/addon/duplicatetab/ or https://addons.mozilla.org/en-US/firefox/addon/duplicate-tab-228106/

Thank you :) ... but i found this feature useful in chrome ... below is the screenshot added....

You didn't mention that in your initial posting and since I have never used Chrome, I was unaware that is was available there. It is a feature in Firefox to stop the inadvertent opening of a duplicate tab, a feature that was added to Firefox in 2011, iirc.

You can middle-click the Reload button (or hold Ctrl and left-click) to duplicate the current tab. The only way to do this with the keyboard would be to use some shortcuts and first set the focus to the location/address bar (command + L) <strike>and select current URL (command + A )</strike> and open the selected text in a new tab (option + return).

(edited to remove select all)

• https://support.mozilla.org/kb/Keyboard+shortcuts
• https://support.mozilla.org/kb/Mouse+shortcuts

On Windows, pressing Alt+Enter in the address bar loads the address in a new tab. It doesn't seem to matter whether the text is selected or not. I think cor-el is referring to the same feature with option/alt+Return key combination on MacOS.

Now... that is NOT the same as duplicating the current tab because it is a fresh load of the URL without the current tab's history and doesn't reflect any modified state of the page (e.g., data entered into a form wouldn't be duplicated).

I don't know which result you are trying to accomplish...

Edit: The way I know to truly duplicate the tab is to hold down Ctrl and then click and drag the tab to a new position on the tab bar where you want the duplicate to be. Probably on MacOS you would hold down Command while dragging.