В Firefox 79.0 при открытии браузера стала на несколько мгновений показываться белая страница с "неразмеченными" настройками расширения, некрасиво: https://i.imgur.com/XXyMnF0.jpg . А так, всё нормально, хорошая Начальная страница.

this addon grabs the cursor focus so you cannot simply open up a new tab and paste to perform a web search ... Please fix

The only app which can replace the background of New tab without modifying .css. This has been an annoying problem for millions of users for about 5 years. On Reddit there are huge pieces of code which advanced users have to put in a special folder in their Explorer and they have to modify program files and they need to have some patience to copy-paste all the code in the right placeswithout re-trying a couple times. This extension finally realized this in a couple clicks. Theere is one problem left, however, your thumbnail icons are going to change their positions and the thumbnails are going to to be googled and re-connected to their links, i.e. this extension does not create thumbnails for sites. All right, another half an hour of work. Look, Firefox devs, I have to go through this torture because the browser doesn't allow its users to change the background of New tab. So, i have had to search for this extension since winter since I switched to a dark theme in Firefox to save my eyes with the dry eye syndrome (and this means they are reeeeally sensitive to light, and I feel sand on their surface when my screen is too bright). And now the other surprise from Firefox devs - when you create a new tab in Firefox, it flashes really bright in white. This leaves my eyes shocked. And to add oil to fire I have 1 hour until I have to wake up to work. You see? I have got insomnia, but i am so frustrated that I decided to waste my cyrcadian rhytms on criticizing and begging you! This should finally be present in Firefox by default. So many users need dark background nowadays. White is the colour of pain.

New Tab Toolsで快適だったのは、Firefox52.9まで。

Firefox55以降のNew Tab Toolsは不具合が多くて使えません。
ピン留めしているのに勝手に移動する。
閉じるを押してもタイルは消えなかったり別の位置へ瞬間移動する。
以前は別タブからＵＲＬをドロップしてタイルの位置に登録できていたのに、ＵＲＬを開いてしまう。
しばらく放置して何日かたつと、タイルに登録されたものが全部消える。アドオンの自動更新のせいかもしれない。
ダークモードにすると、文字が識別できない配色になる。読めない。

can't backup!

Great addon - can't find anything else that does the job. However, tiles are prone to randomly disappear from the page when rearranging them with no way of getting them to reappear again. Can't recreate the tile because the addon thinks the disappeared tiles are still there.

Good stuff.