This is a very strange thing to be happening if you are using your center mouse wheel to scroll (I presume that you did not really mean mouse button).

Using the mouse wheel to scroll works perfectly on my machine running Firefox 57.0.1, but if I hold down the left Ctrl key and use the mouse key, then I do get the magnify effect up or down, depending on which direction I scroll (although when using this, the page itself does not scroll).

What sort of mouse are you using and do you have a setting page for it (like Logitech Options for example)? I am wondering if you somehow have a Ctrl key stuck down on your keyboard or something of that nature.

I just did a little test using Notepad. I just opened a fresh Notepad, made a line of random text and copied it lots of times to bring up a scroll bar for the file. I can then use the scroll wheel on the mouse to scroll up and down the text. However, if I hold down the Ctrl key and try the mouse scroll, it does not work on the Notepad file (i.e. using the same action that is one of the methods of doing the magnify in Firefox). Perhaps you might like to try that test too?

Do the up and down arrow keys on your keyboard work to scroll the page properly?

Many of the things you speak of, I don't really understand. I've tied everything to stop it. I might add that here in Austalia we are changing to a fibre optic system. I've yet to connect to that to date> It's very annoying. just tried the ctlr key and it still does the same thing. Perhaps it's the difference of wireless versus Fiber Optic????????????

Just by clicking the left click to respond you your comment has reduced the size of the text. Damn and bouble damn.

Are you using a wired or wireless mouse?

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

I apologize for not writing clearly enough for you to understand in my last post. Please do as @FredMcD advises so that we have a better idea of what might be going wrong. Thank you.

Thank you all. It's so kind of you to try to help me. First thing this morning, I could not gain access to my banking system. Logged out and went to Facebook and the same magnification etc. was happening. Ho hum I thought. As quickly as it came, it suddenly stopped doing it. It's as though the laptop is attempting to put me a Lunatic Asylum. I'm most grateful to all of you for taking the time to read and then experiment. Thank you, Elizabeth Schuit.