^^ toMACsh, the browsers were redirecting me from various webpages, e.g., a university webpage, a church webpage----nothing sketchy about the webpages from I was redirected. Even my homepage, which had been set to Google in the browser preferences, got changed to Yahoo.
^ bobtomay, I think you might be right about the browser extensions and add-ons.
On the browser menu bar, I found tabs for Amazon and eBay that I didn't put there myself. When I checked the extensions/add-ons, I found the Amazon and eBay add-ons. These apparently were linked to Spigot extensions:
Uninstall Spigot Mac Extensions - Spigot
Apparently, the Spigot extension installed a Searchme/Yahoo extension:
https://apple.stackexchange.com/que...hme-extension-for-safari-and-chrome-come-from
The only app I tried to download recently was the financial program, Mint. I think it was from the CNET site.
That Spigot extension functioned just like malware I've seen on Windows PCs---hadn't experienced anything like that on Macs before.
I removed the suspect extensions and, so far, things seem to be back to normal.