I just saw this comment, and I can tell you how to turn it off permanently. You need to go to the Search settings link (visually, it appears as an item in a menu that pops up when you click a button with a cog symbol on it after you've done a search; I'm not sure how it shows up in screenreaders). On that page, there's a section for "Google Instant predictions", with the question "When should we show you results as you type?". You need to change that to "Never show Instant results", then click the Save button at the bottom.

The page doesn't seem to use standard radio buttons, oddly, but the ones they do use seem like they should be accessible.