Middle Click Scroll Selects Cells

I just started using the browser version of Excel because it's more convenient than the desktop app with Sharepoint. Immediately, I noticed that middle clicking to scroll horizontally selects the cell under the cursor. This completely wrecks my workflow because I will lose my selection. I can't feasibly use the horizontal scroll bar because...

A) The spreadsheets are way too big and the scroll bar is too sensitive.

B) Torture is not permitted at my company.

How do I disable this bizarre behavior?