Could you start by disabling any suspicious extensions? You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then cast a critical eye over the list on the right side. All extensions are optional. If in doubt, disable.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Next, please check for a user.js file, which can override your preferences at every startup. This article has a section on the user.js file: How to fix preferences that won't save.

jscher2000 said

Next, please check for a user.js file, which can override your preferences at every startup. This article has a section on the user.js file: How to fix preferences that won't save.

As I only just less than an hour ago  ( 07.00AM   overhere)   managed to get rid of Bing   (I hope   ! )   in exchange for Google,   I thought it might be wise to follow your advice to  'slimmer'
After opening the profile folder I did not see any user.js files,   which is a good thing,   right   ?
But what really gave me a scare:   this whole long list of   'things'   (I haven't a clue what to call them):   all dated   8-8-2016   (a little after 07.00AM)  and taking up so many kB's ,   like   e.g.:
places.sqlite   --   20.480 kB   !!!
And I wonder now:   have I done something wrong   ?

(edited a typo)

Happy112. A quick partial answer to your question.

I am sure jscher2000 will be pleased to fully answer your question; along with the inevitable follow up questions, but would you mind starting that as a new question of your own, {Please use /questions/new/desktop ) and then posting back here to say you have done so. (jscher2000 will be able to find your new question easily, or you could provide the link to it yourself.)

The file places.sqlite is in all Firefox profiles and is quite normal. The file is a database of Bookmarks, History & Downloads. The other things are part of your profile. and it is probably not a good idea to mess with them unless you are following specific instructions, It may however be prudent to back up the Firefox profile occasionally. See also

• Profiles - Where Firefox stores your bookmarks, passwords and other user data
• http://kb.mozillazine.org/Places.sqlite
• Back up and restore information in Firefox profiles

As for Bing/Google

• Add or remove a search engine in Firefox
• Change your default search settings in Firefox

I believe you have the Dutch version of Firefox, I thought that may still have used Google by default, but I did not try checking.

P.S. If you try to follow the instructions for providing information as you post your question the forum software will list all your addons, and try to detect whether or not you do have a file user.js

John99 said

Happy112. A quick partial answer to your question. I am sure jscher2000 will be pleased to fully answer your question; along with the inevitable follow up questions, but would you mind starting that as a new question of your own, {Please use /questions/new/desktop ) and then posting back here to say you have done so. (jscher2000 will be able to find your new question easily, or you could provide the link to it yourself.)

John99,
Thank you;   that was reassuring enough for me not to post a question about this.
'Just found out that,   when your laptop works on Windows10 and has just been updated,   there is absolutely   no way   to get rid of that duo   Bing/Edge   ....... (worked before the update)
Now maybe   this  is what I should post a new question about:   Why would you even want to get rid of Bing/Edge    ?
Cause I've just asked myself that question,   and came up with the answer:
You don't have to either use Bing nor Edge;   as long as you have   Google/Firefox   you can just simply ignore that other couple.
Windows does have some perks;   just use those .
But getting rid of Bing as your homepage when you're using the   'E'-tile in Windows:   forget it    !
I was so adamant to try and do it,   but I've now convinced myself:
I don't   have  to   !
I can only hope that this is helpful to   'slimmer'   (?).
Cheers,
Happy112

John99 said

As for Bing/Google

• Add or remove a search engine in Firefox
• Change your default search settings in Firefox

Adding or removing a search engine in Firefox:   piece of cake,   (as is changing your default settings)  --   it was really though after this last update,   but it's   'doable'.
But you '&nbsp cannot   do it when you're using the Windows start button.
Microsoft now even placed the   'Edge-icon'  on the task bar;   never used to be there before   .....
And that's not all this update has changed   (nightmare   ! )

Windows & Edge questions would best be addressed if you try a Windows forum examples

• tenforums.com
• windowssecrets.com/forums/

Although it is otside the scope of this forum I will briefly mention you could consider trying something like clasic shell if you do not like the big dynamic display of tiles from Windows 10 start menu.

• classicshell.net

John99 said

Windows & Edge questions would best be addressed if you try a Windows forum examples

• tenforums.com
• windowssecrets.com/forums/

Although it is otside the scope of this forum I will briefly mention you could consider trying something like clasic shell if you do not like the big dynamic display of tiles from Windows 10 start menu.

• classicshell.net

Microsoft   (Bing/Edge)   would not let   Firefox   do   it's thing   .......

Posted a question about it at the   Microsoft support community   first   .......

By the way:   the topic of this thread was   Bing   (well,   partly)   ........