One possible culprit would be an extension. You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions.

Then cast a critical eye over the list on the right side. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything that mentions search, or looks suspicious, or that you just do not remember installing or why? If in doubt, disable (or remove).

Please keep track of potential problem add-ons for reporting.

Any improvement?

Thanks - I've disabled an extension called PDF 1.2.1, which looks fairly innocuous but is the only thing there ... and I think that might have resolved it.

Would you imagine that this is a "quirk" or malware?

In addition to the above, please see :

https://novirus.uk/search-yahoo-com-redirect/

Hi DVID, malware takes many forms, and sometimes arrives as part of a bundle with other things...

Does PDF 1.2.1 have an enabled "Remove" button? If so, that might be simplest, but if you want to learn a little more about, you could try:

(1) View the extension's details page by clicking the "More" link below it's title on the Add-ons page

(2) Search the extension's unique ID, which you can find on the Troubleshooting Information page. Either:

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

Scroll down past "Application Basics" and "Firefox Features" to "Extensions".

Then you can triple-click the entry in the ID column, right-click, and search your default search engine for that code. Sometimes sites that scan questionable add-ons will come up. Other times, nothing comes up because it's either too new or the authors keep changing the code.

If the extension does NOT have an enabled Remove button, it was installed in a shared location. This can help track down how it arrived on your system, but you'll need to dig into yet another file.

In the first table on the Troubleshooting Information page, on the Profile Folder row, click the "Open Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Find a file named extensions.json and drag-and-drop it into the tab with the Troubleshooting Information page. After a few moments, Firefox will display a structured view of the file contents. You might need to expand it to see the details for the extension. You can use Find (Ctrl+f) to look for defaultlocale to jump to the title of each extension, then for the suspect one, look at the address next to path (due to file format requirements, each \ is doubled, but when exploring your disk, you would use a single \ as usual).

Thanks. I've removed it already but I guess it would have been nice to establish what was going on.

I wonder if I'm being naive to think "Well, it's working as normal so all should be okay"?

Think of an unknown extension as being like a strange object in your house. You would be suspicious of how it got there and you might check all the locks.

Thanks - that's a good analogy.

I guess I'm trying to decide if I need to do anything else (throw computer into the sea??) now that the problem *appears* to have gone and all the Norton scans I've done have found nothing?

We do have a support article listing other tools Firefox users have found helpful in the past. They are free or "free trial." Let your paranoia be your guide... Troubleshoot Firefox issues caused by malware.

....... and maybe take a look at the link I posted earlier :

https://novirus.uk/search-yahoo-com-redirect/

Thanks McCoy. To be honest, at the time of your post, I was probably too paranoid to click on any links!

DVID said

Thanks McCoy. To be honest, at the time of your post, I was probably too paranoid to click on any links!

Totally understandable, considering the circumstances  !