There’s no going back!
Correction: Apparently I said “right” when I meant “left”.  Which rendered my little joke incomprehensible. Serves me right for writing my post too fast — and for trying to make dopey jokes!
Because the right-arrow left-arrow key on my keyboard is broken.
So… Can’t go back.  Right?
Yeah. You had to be there.
I sure hope I don’t have to buy an actual entire new laptop just to get my habitual navigation buttons back.
I popped off the key covers to see if I could see anything preventing the switch from contacting.  Only dust, which I removed, and which made no difference.
It might have something to do with the coffee I spilled on the arrow-keys the last time I was at Starbucks.
Just a hypothesis, of course.
ADDENDUM: Apparently I forgot to mention that my computer is a laptop.  I realized this when people started telling me, “Hey, why don’t you just get a new keyboard? They’re cheap!”
Because, hey, it’s a laptop, not a desktop.  Which I failed to mention.
If the lack of a back-arrow becomes too annoying, I can always go the route of using my laptop AS a desktop by plugging in an entire separate second keyboard… let’s hope it doesn’t come to that.