Does it help if you try Firefox's safemode. For instance hold the Option key (Shift Key in Windows) whilst starting Firefox

• Diagnose Firefox issues using Troubleshoot Mode

Please post back with how you get on.

Try to delete the search.json file and possible search-metadata.json and search.sqlite files in the Firefox profile folder to reset the search engines to the default.

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Firefox will rebuild the search.json file from the default built-in search engines that come with Firefox and the searchplugins folder in the Firefox profile folder.

John99 said

Does it help if you try Firefox's safemode. For instance hold the Option key (Shift Key in Windows) whilst starting Firefox

• Diagnose Firefox issues using Troubleshoot Mode

Please post back with how you get on.

Holding the option key as I start firefox does not get me into safe mode. The triple bar menu icon does not work, although the headings on the menu bar at the top of the screen work. So I can't get into safe mode. Suggestions?

cor-el said

Try to delete the search.json file and possible search-metadata.json and search.sqlite files in the Firefox profile folder to reset the search engines to the default. You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Firefox will rebuild the search.json file from the default built-in search engines that come with Firefox and the searchplugins folder in the Firefox profile folder.

clicking on "troubleshooting information" on the help menu produces no response. I also tried starting finder holding down the option key, then clicking on go holding down option key, then opening library, but once there, I don't find a firefox or mozilla folder, nor does a search for "search.json" yield any result.

Sorry you are having so many problems.

This article explains how to find the Firefox profile location without needing to use Firefox.

• Profiles - Where Firefox stores your bookmarks, passwords and other user data_finding-your-profile-without-opening-firefox

In fact I think you will need to create a new profile, and afterwards try to replace some of the data and settings

• Profile Manager - Create, remove or switch Firefox profiles

Please create a new profile, accept the location suggested and use short name like new-2016-001 . Please do not attempt to delete or rename any profiles without asking first. It is too easy to make mistakes and lose data or passwords. Opening the profile manager lets you choose which profile to use.

Please post back with how you get on. If the new profile does not give you a working Firefox the next thing to try is a clean install including removing the program files.

After creating a new profile you will need to follow the instructions in this article

• Recover important data from an old profile

Clean Reinstall

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

To do a clean reinstall of Firefox, please follow these steps: Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

Advisory note from a moderator: Please take care see my #answer-860549 . The profile should be renamed rather than deleted or you lose data such as passwords and bookmarks. Using the built in profile manager #answer-860542 to create a new profile may have been a better solution for most people. ~J99

Hello, Thanks to some other helpful replies, I found a solution. I deleted my profile in profile manager. I followed the instructions in one of the help pages that gave a an instruction to get to the profile manager using the Terminal program under utilities in applications, and then, once the terminal starts, pasting in this link: /Applications/Firefox.app/Contents/MacOS/firefox-bin -profilemanager Then, once it loads, delete the present profile. Profilemanager will afterwards create a new profile. Then exit out and re-start mozilla. You will have to sign in once again, but when I did, the program was restored and worked fine. Then close the terminal program. The accompanying article http://kb.mozillazine.org/Profile_Manager, warns you to be careful of what you do, and you probably should review it before trying this.

Glad you found a solution, and thanks for posting back.

However that would not have been recommenced as a solution. You could have instead renamed the profile. That would recreate profile without deleting the original.

You have now lost all profile information. Profiles - Where Firefox stores your bookmarks, passwords and other user data So unless you backed up the profile first, have some other backup, or can get it out of the time machine you have lost password & bookmarks etc.