Windows 7: Why does my screen shrink?

I am innocently typing while my browser in firefox is open, and all of a sudden my screen shrinks. Then it enlarges, then it shrinks, then it permanently shrinks so that every time I open the page, it is so tiny! How do I correct?

To start try this

Downlad and run a scan with malwarebytes
http://www.malwarebytes.org/mbam.php

Scan for virus

Check your graphics card and driver

bad answer.. a new computer. And I don't want to pay for virus scan I already have. something is going on with the magnifier. just dont know what to do about it.

Do you mean, that if you clikc on the enlarge box on the upper right, it goes back to naormal? If yes, I misunderstood your question.

Thanks Rich. I am new to windows 7, last os was xp.

This has happened a few times. I am typing, for example, in outlook (an email), or through my server (an on line email), or in a closed server. All of a sudden, the type is reduced to about 4 points, then it will enlarge, then reduce etc. It must have something to do with either the magnifier, or a command that I am accidentally giving (I type fast). But I don't know what it is.

When it happened before, I was able to fix, but don't remember how..except somehow I was able to reset to 100% view. It is very annoying.

What's worse, when I close firefox, then reopen, whatever program I was using when it shrank, is still shrunk. But if I go to explore, it is normal size. So do you know anything about this? I can't be the only one this has happened to.

Sounds like you hit the window key and then plus or minus.. Can that be it?

Ok, now we are talking. I hit windows, then shift+ and it went back to normal. Thanks!!

We started off with a misunderstanding, but I am glad that it worked out.

There is nothing that cannot be resolved with good communication. LOL

Take care my friend, and I hope all the email brings good news.