You can set <b>layout.css.devPixelsPerPx</b> to 1.0 (default is -1) on the <b>about:config</b> page. Adjust its value in 0.1 or 0.05 steps like 1.1 to enlarge or 0.9 to reduce until icons/text looks right. You may need values above 2.0 if you have a high resolution display but make sure not to use values too large or too small. *modifying <b>layout.css.devPixelsPerPx</b> affects user interface and webpages (global zoom) Firefox has a Zoom section in Settings to set the default zoom level for webpages. *Settings -> General -> Language and Appearance -> Zoom You can open the <b>about:config</b> page via the location/address bar. On the warning page, you can click "Accept the Risk and Continue"to open about:config. *https://support.mozilla.org/en-US/kb/about-config-editor-firefox