Was there really a user.js file in the profile folder?

Did you check its content in a text editor to see what prefs are initialized?

Is only this pref affected?

• network.prefetch-next

I attach You the screenshot!

It's TWO modifications. I reset to the default but this resetting it's NOT saved

Changes you make in 'about:config' are saved after you close and restart Firefox.

If a change is not saved, you may have something installed that is changing the preference back each time you restart Firefox.

And you'll need to find out what that is - maybe your 'Internet Optimizer'  ?

You didn't confirm if there is a user.js file in the profile folder with "user_pref();" lines, so could you please answer my question?

Do you lose these pref settings when you close Firefox and reload Firefox immediately or only after you have rebooted the computer?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen or hold down the Shift key) to see if that has effect.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

i not remember, but the user.json file was in Firefox...

I deleted it and yet I not find

Hi,

I find one other user.json file in my Bitdefender Agent setting: WinUsers.json

Can I delete it?

Just leave this WinUsers.json file in place and the file name isn't user,json, but user.js (Windows wrongly would see it as a JScript file).

Thanks,

I think, I find the "problem". My UBlock Origin settings disabled pre-fetching...

The Bests!