sempre usei

It is all right now.

No longer works in Firefox 61.0.1

sympa

Always used this, can't have Firefox without it

only displays thumbnails for results from youtube, the rest are empty

It works, but the thumbnails are too small to be helpful and can't be enlarged (would be great if they could be zoomed on mouseover). Also, many sites just show their login page as the preview (e.g. Reddit and Github). What I'd really like to see an addon do is force the search result links to show the whole title of the linked page, instead of just the first several words. If that ability were added in addition to zoomable previews, this addon would be great. As it is, it's not worth keeping installed.

Nil so far