Any idea where you picked up the Sammsoft Toolbar extension? A web search indicates that it could be unwanted software.

Try disabling it here:

orange Firefox button (or Tools menu) > Add-ons > Extensions category

If a link appears above the extension after disabling, click that to restart Firefox and complete the process.

Does that make any difference with your new tab button?

Other resources:

• Troubleshoot Firefox issues caused by malware (links to supplemental scanners)
• How to fix preferences that won't save (remove user.js file)

You can use the SearchReset extension to reset some preferences to the default values.

• https://addons.mozilla.org/firefox/addon/searchreset/

Note that the SearchReset extension only runs once and then uninstalls automatically, so it won't show on the "Firefox > Add-ons" page (about:addons).

Note that your System Details List shows that you have a user.js file in the profile folder to initialize some prefs on each start of Firefox.

The user.js file is only present if you or other software has created it, so normally it wouldn't be there. you can check its content with a plain text editor if you didn't create this file yourself.

The user.js file is read each time you start Firefox 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.

• http://kb.mozillazine.org/Preferences_not_saved

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

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)