Maybe you hit a key or key plus mouse button inadvertently. You can enlarge the page with ctrl-+.

Reset the page zoom on pages that cause problems: <b>View > Zoom > Reset</b> (Ctrl+0 (zero); Cmd+0 on Mac) *http://kb.mozillazine.org/Zoom_text_of_web_pages

Update All your Firefox Plugins * https://www-trunk.stage.mozilla.com/en-US/plugincheck/ * http://www.mozilla.com/en-US/plugincheck/ ** Remove Checkmark from Downloading other Optional Softwares with your Plugins (e.g. Toolbars, McAfee, Google Chrome, etc.) Clear Cookies & Cache * https://support.mozilla.com/en-US/kb/Template:clearCookiesCache Clear the Network Cache * https://support.mozilla.com/en-US/kb/How%20to%20clear%20the%20cache#w_clear-the-cache Check and tell if its working.