Does it make any difference to click in between a couple results (to ensure that Firefox gives focus to the document) before scrolling?

I think it's possible for a web page to capture and discard scroll wheel input, but as far as I know, Bing doesn't do that. Do you know whether you have any extensions that modify how pages scroll, or might create an element in the page that intercepts wheel input?

Hello. Sorry, no. Clicking on the result list has no effect whatsoever.

However, I have noted that mouse wheel scrolling is correctly executed if the mouse pointer is over an ‘image section’ in the result list. This is indicated in the enclosed screen capture.

To my knowledge I have no extensions which could affect scrolling.

For the images section, does the wheel scroll the image section to the right/back to the left, or the page? If it scrolls the images, maybe the page thinks the Shift key is being held down (holding Shift switches the wheel from vertical scrolling to horizontal scrolling).

I understand fully your comments in regard to the use of the Shift key whilst scrolling.

To be explicit as to my experience of this particular scrolling irregularity :

'Search result lists' can contain a section which is denoted 'Images' (in Bing). If so then this section is always high up in the 'search result list', usually first I think, and contains an array of images. (As in the example I included in my last post, but note that in that example the array of images was not first in the 'result list' but second)

When the mouse icon is over the 'search result list', but 'outside the image array area (boxed in my example), and vertical scrolling is attempted using the mouse wheel then scrolling does not occur.

If however the mouse icon is over the 'search result list', and 'inside the image array area' and vertical scrolling is attempted using the mouse wheel then scrolling occurs correctly whilst the mouse icon remains 'within the image array area'. The scrolling which takes place is of the 'entire result list'. This is the expected result in my experience. The 'entire result list' is scrolled vertically, not just the 'images within the boxed area'.

In regard to horizontal scrolling, with the mouse wheel, this is a function I have not previously used (to any greater extent). This entire post is in regard to vertical scrolling only as it is this functionality which is not working as it should.

Some things defy explanation. The scrolling irregularity I have been experiencing has ceased to exist some time during the latter part or the day here in Sweden. It's beyond me. Admittedly Firefox update 143.0 was installed earlier today but my scrolling problems continued after that, yet now everything is running just fine. I'd still be interested if anyone can point to any plausible cause for these problems.