When you say they disappear, what happens? Do they turn into white-on-white text, or that area is blank amidst the surrounding text, or that area is gone?

I've had no chance so far to try it out on any pages where background is not white. With a white background, I cannot tell the difference between the three possibilities that you indicated. The fact is that when I return to the page after clicking a link, I see just the white background where the link was seen before clicking. But if I click on that empty spot, the link re-appears for a quick moment, only to bring me immediately to the site to which it links. When I return back to the original page by pressing "<-", I see again only the empty space where the link was.

(I would add that this does not happen on the same sites when I use different browsers, like IE)

That's interesting. The normal color for visited links is not white (I guess it's a shade of purple). Can you think of any add-ons or settings changes that could be affecting link colors?

I'm sorry I'm failing to explain it. The links are a shade of purple, exactly as you say. The background is white. When I click a link, it takes me to the site to which it links. When I go back to the page where I clicked it, I see just the white background on the spot where I had seen the link. When I, then, place the mouse on the spot where I had clicked the link, and make a click on this empty (=white) spot, the purple-colored link appears for a quick moment, only to take me right away to the site to which it links. When I go back, I do not see it again.

Thanks, it's hard to imagine what causes that.

If you right-click a blank area of the page and Select All, can you see the text of the missing link? If you can see the text, is it in the same font (typeface) as the rest of the page or does it appear to be in a special/different font?

Do you use a "high contrast" theme for Windows? If so, Firefox will try to adapt to it. You can turn that off as follows:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

Firefox 56-58: Scroll down a bit to the Language & Appearance section, and click the "Colors" button.

Firefox 38-55: In the left column, click Content. Then on the right side, click the "Colors" button.

In All Versions: Change the "Override the colors specified by the page with your selections above:" setting to "Never". Then click OK.

Any difference?

Interestingly, I do not have this problem at work, where I have Firefox under Windows 7. If my Firefox at work gets the same updates, the problem must come from the interactions of the updated Firefox with Windows 10, which I have at home. I will try what you suggested when I get home.

"If you right-click a blank area of the page and Select All, can you see the text of the missing link? If you can see the text, is it in the same font (typeface) as the rest of the page or does it appear to be in a special/different font?"-- Yes, I can see it then, and it is in the same font as the rest of the page. But when I deselect all by left-clicking it disappears again.

"Windows: "3-bar" -- where is that? I'm not sure I understand the meaning of the rest of the instructions. I.e., what cause of the problem they assume as a hypothesis.

The application menu button at the right end of the main toolbar has 3 horizontal bars on it. Hard to describe.

The change is relevant if you use a high contrast theme.

Thanks a lot! Yes, this was the problem: the Color for Visited Links was set as white (i.e. the same as the one for Background). It looks like most pages I visit do not specify the colors, so setting Override to "Never" does not make any difference;, but changing the color for Visited Links does. Thanks again!