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We'll explain errors such as "Server not found" or "Unable to connect" and how to fix problems where Firefox can't access websites but other browsers can.

This article describes problems where Firefox cannot load websites but other Web browsers (such as {for win}Internet Explorer or Microsoft Edge{/for}{for mac}Safari{/for}{for linux}Epiphany on Gnome or Konqueror on KDE{/for}) can. When this happens, Firefox may show a ''Server not found'' or ''Unable to connect'' error message. * For other error messages that display when you try to view websites in Firefox, see [[Websites don't load - troubleshoot and fix error messages]]. * If none of the Web browsers on your computer can load websites, see [[Firefox and other browsers can't load websites]]. __TOC__ = Internet Security software blocking Firefox = If you were able to load websites until you updated Firefox or until your Internet security software was updated, reconfigured or a new one was added, your Internet security software (including firewalls, antivirus programs, anti-spyware programs, and more) is likely preventing Firefox from connecting to the Internet. {note}'''Note:''' Some Internet security programs can block Internet access even when they are in a "disabled" state.{/note} In general, you should make sure your Internet security software is up-to-date and remove Firefox from your program's list of trusted or recognized programs, then add it back. For instructions on how to configure some programs, see the [[Configure firewalls so that Firefox can access the Internet]] article. = Firefox connection settings = If you connect to the Internet through a proxy server that is having connection problems, you will not be able to load websites. To check your [[Connection settings in Firefox|connection settings in Firefox]]: # [[T:optionspreferences]] # In the {menu General} panel, go down to the ''Network Settings'' section. # In the ''Network Settings'' section, click {button Settings…}. # Change your proxy settings: #* If you don't connect to the Internet through a proxy (or don't know whether you connect through a proxy), select '''No Proxy'''. #* If you connect to the Internet through a proxy, compare Firefox's settings to another browser's {for win}(such as Internet Explorer — see [https://docs.microsoft.com/en-us/internet-explorer/ie11-deploy-guide/auto-configuration-and-auto-proxy-problems-with-ie11 Microsoft's guide to proxy settings]){/for}{for mac}(such as Safari — depending on your OS X version, see [http://support.apple.com/kb/PH7050 Mac OS X 10.6: Enter proxy server settings], [http://support.apple.com/kb/PH4069 OS X Lion: Enter proxy server settings], or [http://support.apple.com/kb/PH10934 OS X Mountain Lion: Enter proxy server settings]){/for}. # Close the ''Connection Settings'' dialog. # [[T:closeOptionsPreferences]] If you find that changes you make to your Firefox connection settings are not remembered when you restart Firefox, see [[How to fix preferences that won't save]]. = IPv6 = Firefox supports [http://wikipedia.org/wiki/IPv6 IPv6] by default, which may cause connection problems on certain systems. To disable IPv6 in Firefox: [[Template:aboutconfigwarning]] # [[T:aboutconfig]] # In the ''Search'' field, enter {pref network.dns.disableIPv6}. # In the list of preferences, click the '''Toggle''' [[Image:Fx71aboutconfig-ToggleButton]] button next to {pref network.dns.disableIPv6} to set its value to {pref true}. = DNS Prefetching = Firefox attempts to speed up loading new websites by using [https://developer.mozilla.org/En/Controlling_DNS_prefetching DNS Prefetching], which can cause page load errors with some system configurations. To disable DNS Prefetching: [[Template:aboutconfigwarning]] # [[T:aboutconfig]] # Enter the preference name {pref network.dns.disablePrefetch} in the ''about:config'' search bar. #* If the preference doesn't already exist, select '''Boolean''' and click the '''Add''' [[Image:Fx71aboutconfig-AddButton]] button. # Press the '''Toggle''' [[Image:Fx71aboutconfig-ToggleButton]] button to set the preference value to {pref true}, if it's not already set. = Firefox cannot load certain websites = If you find that Firefox can load some websites but not others, {for win}first{/for} clear your Firefox cookies and cache: [[T:clearCookiesCache]] == Check for malware == If clearing your cookies and cache did not enable you to load the websites that did not work in Firefox, you should check your computer for [http://wikipedia.org/wiki/Malware malware]. Certain types of malware are known to target Firefox and can prevent it from loading various websites: * If you have an antivirus or Internet security program, update its detections database and do a full scan of your system. * If you still have problems, follow the instructions in [[Troubleshoot Firefox issues caused by malware]]. = Check if an extension is causing the problem = A Firefox extension could be causing the issue, especially the ones that have network access and/or those that rely on manipulating webpage content. Try disabling your extensions in the Add-ons Manager one by one and then reload the page. See [[Disable or remove Add-ons]] and [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]] for more information. <!-- MZ credit --> <br/> <br/> '''''Based on information from [http://kb.mozillazine.org/Error_loading_websites Error loading websites (mozillaZine KB)]'''''