Summary Box for Wikipedia by Dominik Fehr, su-pa

Select or double-click a term on any website and a small popup box appears next to it with an instant Wikipedia preview: the article's summary, its image and a link.
If the term is not an article, or not a clear one, the box offers a search field instead of giving up.

What it can do

• Any term on any website. Select it or double-click it.
• A summary box with the article's first lines, its thumbnail and a link.
• A search field when the answer is not clear — nothing found, a "may refer to" page, or only a near miss. Pick from the results and read them in the same box.
• Favorites: star an article and get it back from the list in the box.
• Follows the language of the page, English as the fallback. Right-to-left too.
• On/off everywhere with the toolbar button or Alt+Shift+W, or for one site only.
• Settings for box width, summary length, font size, images on/off, and an "only while Alt is held" mode so selecting text to copy it does not open a box.

Quiet by design

The box lives in a closed shadow root, so the website's CSS and scripts cannot reach
it — and it cannot disturb the page either. A cache and a debounce keep a term at one
request or none.

No accounts, no analytics, no server of ours.

Why does it ask for "access to all websites"?

Because the box has to be able to appear on any page you are reading — that is the
whole feature. What it does with that access is narrow:

• It only reacts when you select a word or double-click one. Otherwise nothing happens.
• It reads the text you selected and the language of the page. Nothing else.
• It does not record which pages you visit, and it does not read page content.
• The only thing that leaves your browser is the word you selected, sent to Wikipedia.

The code is open source (GPL v3), so you can check all of this yourself.