The built-in feature will divert a new window to a new tab instead. However, if the link is not specially coded to open in a new window, it will just open in the same tab.

Many websites have an option to code links specially to open in a new window/tab. For Yahoo, see: https://search.yahoo.com/preferences/preferences -- this may be saved in a cookie, so if you clear cookies often, you may want to bookmark this address

Otherwise, Firefox doesn't have a setting to "open every link in a new tab instead of the same tab". If you prefer that behavior, there is an add-on: https://addons.mozilla.org/firefox/addon/open-link-with-new-tab/ -- you need to set its options after installation in order for it to do anything

Why are you running Firefox 61?

If you do not want to use Firefox 62, the other version that is current with security updates is the Extended Support Release of Firefox 60. See: Switch to Firefox Extended Support Release (ESR) for personal use.

I am confused. Literally until a day or two ago, all links opened in tabs. I'd changed nothing.

Anyway, I'm running the immediately previous version (61.0.2), but this problem seems to be independent of the version as I've tested it with both.

Maybe you were using an add-on before and it stopped working after the downgrade. Anyway, see my first reply for next steps.

Oh, I should have been more clear. I'm only talking about my desire for new tabs on Yahoo searches, which until a few days ago is what was happening. I just removed and then redownloaded the add-on, which didn't do anything. Then I simply closed out my browser and then opened a new session, and that seems to have done it. How long it will stay this way I don't know.

The only time I ever log in to my personal Yahoo account is for Flickr, so the preferences shouldn't matter, as I log out of Yahoo's main site whenever I want to do searches. So unless it's not setting the preferences back after logging out, I don't know. In fact, I think I may have already had preferences set to open in a new tab when logged in, so it'd be weird if the problem is it's "sticking" for it to revert back to opening search links in the current tab.

Oh, also, downgraded because I was having even more graphic problems (getting black and/or choppy screens when scrolling websites with lots of photos, etc.) than I've been getting, so it became untenable. But that's neither here nor there.

I don't use Yahoo enough to know the interplay between logged-in and logged-out preferences, but generally speaking, logged-out preferences are saved in cookies.

Okay, did a bit more intensive digging. For reasons I can't understand, when I log into my Yahoo account to access Flickr, and then log out of the main Yahoo access for whatever reason it switches the default back to "open in same tab." This did not seem to be happening until a few days ago. I'm still not 100% sure if this is something wrong with the add-on and how it works in Firefox, or if it's solely a change on Yahoo's end.

In any case, I guess you can mark this as solved and close it.

Maybe there's a similar Flickr setting? Anyway, I think only you can select a solution, so it's your call on that.