On its search pages, Google™ captures all plain key strokes to stuff 'em into the search input box. This breaks the single key commands feature of Opera, if you – like I do – enabled this legacy feature in the advanced settings section and like to use it. But there is help available: a UserJS that ”unbreaks“ this Opera feature on Google pages.
There are plenty of single key commands available; let me mention ”1“ and ”2“ which select the previous or next tab, respectively, or another number key ”6“, which sets zoom back to 100%; another useful command is the ”i“ to toggle through the image loading/showing strategies; not to forget ”z“ (or ”y“ if redefined for some keyboard layouts) ans ”x“ as quick back and forward commands.
