Looks you have some software (malware) that wants to modify Firefox and gives you the Firefox 61.0 user agent. You can reset this pref by clicking the trashcan icon at the end of this line. *https://support.mozilla.org/en-US/kb/about-config-editor-firefox ---- You can check for problems with preferences if this doesn't stay. You can delete possible user.js and numbered prefs-##.js files and rename/remove the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in current Firefox releases. You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the <b>about:profiles</b> page. *Help -> Troubleshooting Information -> Profile Folder/Directory:<br>Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data You can do a malware scan just to be sure. *https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware You can also check for the presence of files in some locations that can be used to configure Firefox. *https://support.mozilla.org/en-US/kb/customizing-firefox-using-autoconfig *https://support.mozilla.org/en-US/kb/customizing-firefox-using-policiesjson