NoSquint

NoSquint allows you to adjust the text-only and full-page (both text and images) zoom levels as well as color settings both globally (for all sites) and per site. NoSquint can override the default text-only and full-page (both text and images) zoom levels for all websites, enforce your own foreground and background colors, remember your zoom levels and color settings per site, automatically applying them when you return, and powerful exceptions mechanism lets you split up or group together sites with URL patterns.

Requirements:

Mozilla Firefox 20.0