Not sure about your laptop but mine has a multitouch pad so that if you drag two fingers on it (like on an iPad/pod/phone) it zooms in or out. This changes the fontsize on some websites. You might need to hold a button down like ctrl or shift as well.
I’ve a Toshiba Satellite (Windows 7) and it’s as nickjb says: if i put two fingers on the pad them move them apart the mouse icon will change to a magnifying glass and the font size will increase. To make smaller, two fingers apart then bring together.
TBH I use an external mouse most of the time…if I hold the crtl button then use the wheel on the mouse it will increase/decrease the font depending on direction
I have a Toshiba laptop using Vista OS. Sometimes when my hand is ested on the keyboard somewhere the font size reduces on the page I am on so that it is barely legible. If I come out and go in again then the small size remains. It does it on the particular site I am on, not all pages/tabs I may have open. Problem is I can’t recreate the issue. I thonk it is something to the ‘mouse’ bit and probably touching another key.