Email access is failing on current versions of both Firefox and Chrome on my PC

MrVXT, Thanks for reaching out. I can certainly understand how frustrating it is to successfully sign in only to be met with an Error 10A message afterward. You've come to the right team of experts to help over social media. As a next step, I'd recommend checking for any email filters or rules that may be affecting mailbox visibility, particularly if you're noticing missing messages. If the mailbox itself appears healthy, performing a Force Resync can often help refresh the connection and restore normal functionality. Please keep us posted on the results, and we'll be happy to continue troubleshooting with you if needed.