Komunitné fórum Firefox

I had once used my computer for my husband when his was down. Now when I'm in my computer in a web site, an example send a recipe to myself, when it comes in my email it comes from his account not mine. I've went on to his unit made sure my computer was not signed on using his account. I think it's coming thru Google but I can't figure what where & what to do about it. I attached an image showing the first account that comes up when going to google. I can go up to change the account to mine. But if I'm in site then send something it still shows his account & any response goes back to him not me. This causes much confusion as you can imagine. Is there a way to make this stop?

I often use the key combination Ctrl+Alt+X in Google Docs when on different devices but it doesn't function properly when instead it brings up the AI sidebar gadget. Removing the sidebar button doesn't really help and it's annoying. So how exactly do I turn off the key combination for the sidebar?