Going all the way back to single digit release numbers, this is the first update in nerly all of the 98 versions to date that there is a problem which needs reporting and/or assistance to resolve.
In all earlier versions prior to 98.0.2, using the navigation keys on a Windows PC resulted in the cursor moving according to the key designation on all web sites. Between the installations of versions 98.0.1 and 98.0.2 no change has been made in Windows 10, except the usual automatic updates from Microsoft.
With the last update the on screen movement in response to a navigation key is unpredictable, particularly on web sites such as Amazon, ebay, and others that list items for sale. With (most) other web sites there appears to be no issue.
Something has changed to cause the browser or operating system to respond incorrectly to keycodes with some, not all, websites
You may have switched on caret browsing. You can toggle caret browsing off/on by pressing F7 (Mac: fn + F7).
- Settings -> General: Browsing
remove checkmark: [ ] "Always use the cursor keys to navigate within pages"
Note that this is a Firefox accessibility feature.
With or without the "Always use the cursor keys to navigate within pages" option selected initially made no difference on the amazon.co.uk web site. On opening the first web page there was no response to any of the navigation keys, changing the page generated "random" responses, such as the down-arrow key resulted in changing browser tab. The random responses remained random rather than repeatable. All other keys resulted in similar unexpected responses.
Going back to the web site later, with the option not selected, the response to all navigation keys is correct.
Moving to ebay.co.uk also finds the correct responses to the navigation keys.
Toggling the setting may have shifted a corrupted value; perhaps it might remain correctly predictable ???