Hello mellington,

See Reset Firefox preferences to troubleshoot and fix problems

Try Refreshing your Browser:-

• To do this, click the menu button at the top right corner of the Firefox window.

• Click the “Help” option near the bottom of the menu.

• Click the “Troubleshooting Information” option in the Help menu.

• Click the “Refresh Firefox” button at the top right corner of the Troubleshooting Information page.

• You’ll be warned that this will remove your browser add-ons, reset your customizations, and revert other browser data to the default settings. Click “Refresh Firefox” to confirm you want to make these changes.

If it doesn't solved your problem, then feel free to ask in Reply Section. Thanks for raising your question in Mozilla Support Forum.

You clearly didn't read my post; because the suggestion you gave could only make the problem FAR WORSE! Your suggestion would have me loose all my add-ons, reset my customizations, and revert other browser data to the default settings. I ask you what is a worse condition: 1) FF resetting my preference to open a tab in the background, to open a tab in the foreground, OR FF resetting ALL MY PREFERENCES AND CUSTOMIZATIONS AND REMOVING ALL MY ADD-ONS AND MY OTHER BROWSER DATA? It is abundantly clear you either didn't read my post (which indicates dishonesty) or are unusually stupid. I'm inclined to believe the former rather than the latter. Shame on you.

You can look at these prefs:

• browser.tabs.loadInBackground (normal links)
• browser.tabs.loadDivertedInBackground (javascript and external links)
• browser.tabs.loadBookmarksInBackground (bookmarks)
• browser.search.context.loadInBackground (context menu: search)

This pref determines whether to open a link in the current tab if this is an empty tab or always open a link in a new tab.

• browser.tabs.loadBookmarksInTabs = true

Another really dumb reply, indicating that either you didn't read my post or are doing something dishonest or for some personal gain. I had no problem figuring out how to change the tab opening default to from foreground to background. That is not the issue if you simply read my post you would know that. Perhaps y ou don't really understand English well enough?

Firefox doesn't normally change prefs that way when you update and when this happens there is usually some other (security) software involved.
You can also check if you have numbered prefs-##.js files in the profile folder.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

You just don't get it. Following your procedure above took literally 10 times as much time as it took for me to correct the problem myself by going to FF preferences and unclicking the box to switch to a new tab immediately. And it 20 times as much time to read your email and write this response here. You have wasted my time and now I reciprocate in kind. In addition, your suggested cause for the initial problem as being some "security" issue, is nonsense. I don't have any malware or even firewall software running on my computer and never have in over 35 years of computing. In other words, I am not using a Windoze computer. During over 7 years of using Firefox I have never before had FF change my tab preference during an update. Please continue emailing me so we can waste each others time some more…