Yes, don't reset your profile. Could you take a look at the sectionOrder preference:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future. Since we are checking/resetting, I feel comfortable mentioning it.

(2) In the search box in the page, type or paste browser.newtabpage.activity-stream.sectionOrder and pause while the list is filtered

On mine, running on Windows 10, there's a single match with this value: topsites,topstories,highlights

(3) Next step:

(A) If the preference has a Reset button (left-arching arrow) at the right end of the row, click that button to restore the default value for your build.

(B) If the preference has a blank value, consider assigning one: Double-click the preference to display an editing field, and change the value to topsites,topstories,highlights then press Enter or click the blue check mark button to save the change.

(C) If the preference doesn't exist -- Firefox shows a bar with Boolean Number String and a plus button -- this could indicate that your build has been modified from the default, maybe by your distribution. You could create a string preference with the above-reference value, but you might also check any forums your distribution maintains for Firefox.

My configuration for browser.newtabpage.activity-stream.sectionOrder is properly defined : topsites,topstories,highlights (default value) by my problem persists even if i try to change it.

This issue is with your distro version. Try downloading Firefox from Mozilla, unzip, and run firefox-bin from the folder and see if you have the same issue.

No, my issue is not due to my distribution : my Firefox installation on my Linux desktop works well for years and is updated regularly with new version (Debian package).

This issue is certainly due to a corrupted file in my profile or an invalid setting but I can't find the cause of the error.

I don't know what is the less drastic thing to suggest:

(A) Temporarily rename the prefs.js file (while Firefox is not running) to return most customized settings to defaults

(B) Reinstall Firefox (over the current installation, no uninstall needed) to refresh the program files in case there is code corruption or a version mismatch in the program folder

You can try "Clear the startup cache..." via the "Help -> More Troubleshooting Information" (about:support) page.

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox

Thanks, my problem is resolved after "Clear the startup cache..." :)