You can use an extension to set a default font size and page zoom on web pages.

• Default FullZoom Level: https://addons.mozilla.org/firefox/addon/default-fullzoom-level/
• NoSquint: https://addons.mozilla.org/firefox/addon/nosquint/

Thank you. Strange they removed it from settings and now require add-one.

You're welcome.

You can still zoom pages via toolbar buttons without an extension, but the above mentioned extensions usually work better.

• http://kb.mozillazine.org/Toolbar_customization

• http://kb.mozillazine.org/browser.zoom.full
• http://kb.mozillazine.org/browser.zoom.siteSpecific
• http://kb.mozillazine.org/toolkit.zoomManager.zoomValues

• https://support.mozilla.org/kb/how-do-i-use-zoom

Tried to get NoSquint but "add-on could not be downloaded because of a connection failure at addons.mozilla.org

Tried 6 times