Steps to replicate the issue (include links if applicable):

• Go to the main page of Wikipedia using the Legacy Vector skin
• Type something to generate search suggestions
• Navigate them with the arrow keys
• Optionally, choose an option with the mouse afterwards

For the purposes of this issue, I will assume that the text originally typed into the search box was "Foo".

What happens?:

The search suggestion is only highlighted after the key is released, and is rarely (if ever) the intended option. Selecting an option with the arrow keys is basically impossible. It's almost like depressing the arrow keys is firing off a continuous stream of input events.

If an option is chosen with the mouse after attempting arrow key navigation, that option is queried, but a different text is entered into the search box. This behaviour only manifests when the mouse is used.

What should have happened instead?:

Pressing the arrow keys should navigate through the suggestions, one after the other.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia): N/A; on Wikipedia.

Other information (browser name/version, screenshots, etc.): Firefox 132.0-mint-1.0