Outlook web interface on a Mac: weird Option key behaviour

Hi all,

I've suffered a new setback in my ongoing battle with Outlook's web interface.

As of the last week or two only, when I have Outlook open in my browser (Chrome on my Mac) and I press the option key, it seems to initiate some sort of keyboard navigation thing where it shows letters under Home, View, etc. that I can press to navigate those menus via the keyboard.

So my question is: How do I get rid of this behaviour?

I use option + delete and fn + option + delete very often while typing to delete word-by-word, and a couple times an hour now I accidentally tap just the option key which suddenly jumps into this navigation thing and stops my keyboard inputs in the message I'm typing until I hit escape to go back to normal.

This amounts to a not insubstantial hit to my email productivity.

Thanks in advance!