Until yesterday evening I could switch tabs in an Excel (Office X) page with option-left/right arrow, but, apparently spontaneously, I no longer can.

It doesn't seem to be a pref that I may have inadvertently toggled, but Excel's documentation is pretty convoluted, so I'm not 100% certain.

Has anybody got an idea of what might have happened?

Thanks.

Got it!

I unlocked some new features in Breeze (Great window management and one of my all-time favorite apps!), and although they usurped Excel's native commands they didn't work in Excel, so I was stumped until other windows began jumping all over my screen to places in which I didn't want them.

I edited the Breeze keyboard commands, and all is Excel-ent in Excel-land again.