You can edit an existing tile and modify its title and URL and possibly add an icon.

• https://support.mozilla.org/en-US/kb/customize-items-on-firefox-new-tab-page
• https://support.mozilla.org/en-US/kb/customize-your-new-tab-page

This information is of no help.

The available space is not fully used. The display is set to 4 rows, 1.5 rows are not occupied.

Additional links should be added, not existing ones changed.

The add tile is not displayed. So the question is: How do I get it displayed again, or is there an alternative option to create additional links.

Problem solved.

The pinned shortcuts can be found in the config file (about:config) in the browser.newtabpage.pinned section:

[{pinned data},{pinned data}, ... ]

The value for the tile to add new shortcuts is "null".

This value was at the beginning of the entry: [null,{pinned data},...]

Comparison with a slightly older Firefox version has shown that this value only works between individual entries. After adjusting to: [{pinned data},null,{pinned data}, ... ] the tile is displayed again and can be used to add new shortcuts.

I cannot understand why and how this value was moved to an invalid location. The problem is now solved, however.

I can only get the add "+" button if there isn't enough history to fill all available tiles. So if there is enough history available and all tiles are filled then the only way to add a tile is to edit one of the automatically filled tiles and pin a website to this tile.

Same problem here. When you say add (pinned data) in front of "null" what exactly do you mean? "Pinned data" consists of javascript instructions which include "url", "label", "customScreenshot" and "baseDomain". Or are you stating the the ACTUAL WORDS "pinned data" should be inserted?

Also, since "pinned data" consists of many lines of javascript instructions, what happens if instructions for the missing shortcut tile is inserted at the END of those instructions?

Thanks.