Your System Delete list shows that you have a user.js file in the profile folder to initialize prefs each time Firefox starts. The user.js file will only be present if you or other software has created this file and normally won't be present.

You can check its content with a plain text editor (right-click: "Open with"; do not double-click). The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session.

You can delete the user.js file if you didn't create this file yourself.

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

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

Windows hides some file extensions by default. Among them .html and .ini and .js and .txt and you may only see a file name without file extension. You can check the file extension (type) in the properties of the file in Windows Explorer via the right-click context menu.

The user.js file has nothing interesting in it. However, the FireFox directory has prefs.js file that has many lines referencing Mindspark toolbar & MindSpark extensions, etc. The first lines in this file are:

1. Mozilla User Preferences

/* Do not edit this file.

*
* If you make changes to this file while the application is running,
* the changes will be overwritten when the application exits.

I tried to find in FireFox where toolbars are added/invoked as well as extensions. MindSpark is not listed where I can find it. I don't want to delete prefs.js as there are a lot of preferences in there that I don't want to lose.

Please advise.

You can remove the lines in prefs.js related to prefs that look suspicious and prefs that might be leftovers from an extension you had installed in the past if you no longer have any such toolbars installed.

What is the content of the user.js file in case you still have it?

The image would not upload. Here are the contents of the user.js file:

user_pref("nglayout.initialpaint.delay", 600); user_pref("content.notify.interval", 600000); user_pref("content.max.tokenizing.time", 1800000); user_pref("content.switch.threshold", 600000); user_pref("network.http.max-persistent-connections-per-server", 4);

user_pref("plugin.state.npcontentblocker", 2);

user_pref("plugin.state.nponlinebanking", 2);

user_pref("plugin.state.npvkplugin", 2);

The last three lines set some plugins to "Always Activate":

• plugin.state (0:Never Activate; 1:Ask to Activate; 2:Always Activate)

user_pref("plugin.state.npcontentblocker", 2);
user_pref("plugin.state.nponlinebanking", 2);
user_pref("plugin.state.npvkplugin", 2); 

I don't know if they belong to Kaspersky and actually have effect.

There is no need to modify prefs like the first 5 lines do, so you can remove the user.js file and reset these prefs on the about:config page via the right-click context menu to the default value or alternatively remove the prefs.js file as well to reset all prefs. Then you do not need to hunt down other prefs that may have been modified by an extension or other software.

user_pref("nglayout.initialpaint.delay", 600);
user_pref("content.notify.interval", 600000);
user_pref("content.max.tokenizing.time", 1800000);
user_pref("content.switch.threshold", 600000);
user_pref("network.http.max-persistent-connections-per-server", 4);

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

Are you using "Clear history when Firefox closes" to clear any personal data?