Lower right-hand corner of Firefox window frame; small white square; green "S" and blue "P." Click = diagonal red line superimposed over letters, upper right to lower left. What is this? What's difference between line and no line?
Nothing appears when I superimpose the cursor over the white square. Next to it is a dark-gray lock-shaped icon which, if I superimpose the cursor over it, tells me if the site I'm on is authenticated. These icons are in the lower right-hand corner of the Firefox window frame just to the left of the three diagonal lines which are used to expand or shrink the window.
Wšykne wótegrona (3)
That is not a built-in feature of Firefox, but will have been added by the SearchPreview add-on that you have installed. For details on what the add-on does see https://addons.mozilla.org/firefox/addon/searchpreview
TonyE --
Thanks for your reply. I have no idea how SearchPreview got installed and will uninstall it as soon as I can figure out how.
You're welcome
In case you have not already figured it out, see https://support.mozilla.com/kb/Uninstalling+add-ons