Firefox browsing carrots?!?

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For the last two days the Firefox install on our home PC has been behaving oddly, specifically moving the arrow keys no longer moves the page as a whole, instead it scrolls through the text like in Notepad, MS Word or something. As it turned out I had inadvertantly turned on caret browsing/navigation where you can move around the page and select content with your keys rather than the mouse. Most likely I accidentally hit the F7 key which turns it on while I was tidying the desk at home, ironically I found out about it while cleaning my desk at work and wiping down my keyboard when I accidentally hit the relevant key. I can see how it would be beneficial at times but I wish there was a status display to say it was turned on/off to at least give a clue to newbies that it was at least possible, so they don't think they're going insane when their computer starts doing something funny. Doh.