Emails Automatically Moved And / Or Deleted

Something is happening when I am using email that I can't prevent.

Messages in my Inbox are automatically getting moved and deleted, without me doing anything.

I access my email on line at netmail.verizon.net

While I am in email, looking at my inbox. I often will get a sort of pop up message. A kind of "moving cursor" appears as a pop up or overlay. It says "moving messages."

There is no option to stop or cancel this.

Sometimes the messages are being moved to my Trash folder. Other times, I can't figure out what has happened to them. They seem to disappear.

I called tech support at my email provider, Verizon. The tech support person checked everything and could not figure it out. The problem does not have anything to do with filters.

She said something in my computer -- some kind of bug-- perhaps something I downloaded, perhaps some program or app, is interfering with my email and causing this to happen. She says the problem is not one at Verizon's end and that they can’t fix it.

I am using Windows 10 and Microsoft Office Home and Student 2013.

I usually access the Internet via Mozilla Firefox.