Here is a screenshot.

The dialogue popped up even though I did not enter any link.

This is a glitch with the new tab page: when Firefox wasn't able to grab a screenshot from the site, it will try to do it in the background so that tile can be populated. It will fail every time with this link so that's a bit dysfunctional in this case.

You need to get rid of that tile. Two options:

(1) Tell Firefox not to show the tile on the new tab page. Hover the tile and look for and X in the upper right corner and click it. More info: Customize your Firefox New Tab page.

(2) Delete history for that site. You can use the Library window as follows:

• Press Ctrl+Shift+h or use the History menu > Show All History
• In the search box at the upper right of the window enter ptt.cc to filter the list
• Delete all the entries

Does that work?

It worked!!! Thank you so much. The pop up window stop showing up after I cleared the history :)