hello, try to press ctrl+0 ('zero') while you're on the page in order to reset the zoom level or in case this doesn't work also go through the other common troubleshooting steps at Websites look wrong or appear differently than they should.

Thanks. Your answer allows me, on my computer, to view my web site at 100%.

But what I want to do is have Firefox fixed so that EVERYBODY who views my web site views it at 100%. I believe there is a bug in Firefox that makes this magnification happen.

it is work correctly see if ctrl button in your keyborad is down and clean your keyboard it may causes this problem

this is not a common bug - your website is already showing to anyone on a 100% zoom level per default. most probably you have mistakenly altered that setting locally while visiting your page in the past (for example by holding the ctrl-key while scrolling)...

Wonderful. So it was because I set a default magnification of my web site with that address in a previous viewing, and Firefox retained that magnification? Very sophisticated of Firefox. Thanks.