From MozillaZine Knowledge Base

This list of the more frequently-encountered issues or problems with Firefox is organized by subject and may include links to MozillaZine forum topics and other external sources in addition to Knowledge Base articles. It is not a complete list of Firefox issues. If you don't find an answer below, you can browse all articles in the Category:Issues (Firefox), use the Knowledge Base Search function, or look through the official list of known issues found in the Firefox release notes.

General

• Firefox will not start up
• Firefox fails to start because js3250.dll or other files are not found
• Error loading websites
• Problems printing web pages (more here)
• Firefox says my profile is in use or that it is "already running but is not responding"
• Firefox hangs, freezes or stops responding
• Firefox CPU usage
• Firefox crashes (an error occurs and Firefox closes)
• Reducing Firefox memory usage ("memory leak")
• Standard diagnostic steps when Firefox is no longer working properly

Installation and updates

• Internet access is blocked by your firewall after updating Firefox
• Add-ons not working or unable to install themes or extensions - Unexpected installation error -203 after an update
• "Java Console is incompatible" message after updating Firefox
• Other Software Update problems, including ""Software Update Failed" and "AUS: Update XML File Malformed (200)" messages
• Unable to install themes or extensions
• Problematic extensions (including those that cause conflicts with other extensions or plugins)
• Problems uninstalling extensions and removing "*.xpi" or "ghost" entries from the Extensions list
• Your Linux distributor releases a patched Firefox but the Firefox website wants to force you to update

Bookmarks and browsing history

• All my bookmarks are gone
• I can't save new bookmarks
• I can't export bookmarks to an HTML file
• When I try to restore a bookmark backup I get the error, Unable to process the backup file.
• Bookmarks and browsing history are not working, back/forward toolbar buttons are disabled

User interface

• Clipboard (cut/copy/paste) not working
• Scrolling with arrow keys no longer works
• Find bar opens when typing in textbox
• Window shakes
• Resizing an oversized window or setting Firefox to allow resizing of popup windows
• Large gray bar or box below the status bar
• Unable to search or add new engines
• Toolbar changes lost or buttons missing including customizations reset on startup, missing back/forward buttons after Firefox 3 upgrade, and other localstore.rdf issues.

Downloading opening or saving files

• Unable to save or download files
• Downloads not visible in Download Manager
• Download error: The associated helper application does not exist when trying to open certain files
• The Download Actions list is empty
• "Do this automatically" grayed-out or not remembered and other issues with file types and download actions
• Opening files using plugins
• Opening files from the Downloads window
• "Open File - Security Warning" on Windows, when launching saved downloads (more here).
• Other Firefox file-opening and download issues

Problems with specific websites or web features

• Websites look wrong
• Images or animations do not load (or images look wrong)
• Quicktime symbol with a question mark replaces Flash content
• Video or audio does not play
• Background music does not play
• Unresponsive Script Warning
• Popups not blocked (Details here)
• How to disable bookmark this page popup
• Why "ALT" text image tooltips do not work in Firefox. (Details here)

Privacy and security

• User name and password not remembered
• Firefox asks for a nonexistent master password
• Websites report cookies are disabled when they're not
• "SSL is disabled" message
• "Could not initialize the browser's security component" message.
• Other errors loading secure sites
• Links to local pages do not work
• "Access to the port number given has been disabled for security reasons."

Other

• Jar:File not found error ("Firefox can't find the file at jar:file:///C:/Program Files/Mozilla Firefox/chrome/en-US.jar!...")
• "Windows cannot find ..." error message (or extra tab/window) when opening Internet shortcut or local HTML file
• Uninstalling breaks file type associations or icons
• "Failed to save the preferences file" error or changes to preferences not saved
• Determining whether Firefox problems are caused by issues related to plugins
• Use IE messages upon opening Firefox (malware issue)
• Firefox.exe always open in the Windows Task Manager and automatically loads on Windows boot up (malware issue)
• Addresses entered in IE open in Firefox
• XPCOM:EventReceiver is not responding message on system shutdown
• Deleting Firefox profile via Profile Manager removes non-Mozilla files

See also

Firefox FAQs