The changes you are describing remind me of Firefox's Refresh feature, which you sometimes will be invited to use by a button indicating that you can speed up Firefox by restoring some default settings. So:

Could you check your desktop for a folder named Old Firefox Data?

If you find one:

Refresh moves your old profile (settings) folder to your desktop inside an Old Firefox Data folder. You can use that to "roll back" the Refresh, but it does involve several steps. This takes 5 minutes, but that may be faster than recovering individual files and loading those into your new profile manually.

Check inside the "Old Firefox Data" folder that Refresh adds to your desktop for a folder with a semi-randomized name. If there's only one, that probably has your old settings and add-ons. If there's more than one, you'll want to work with the one that was updated most recently.

Once you have identified the profile folder you want to restore, here is my suggested "old profile resurrection procedure":

Overview

These are the steps described in more detail below:

1. Create a new Firefox profile
2. Remove everything from that new profile folder
3. Copy in everything from the old profile folder

Create a new Firefox profile (Windows)

Exit Firefox completely, and then start up in the Profile Manager by pasting the following into the Windows search box, or the Run dialog, and pressing Enter:

firefox.exe -P

Note: Any time you want to switch profiles, exit Firefox and return to this dialog.

Click the Create Profile button, assign a name like OldSettings, and skip the option to change the folder location. Then select that new profile in the dialog and start Firefox.

Open the New Profile folder in Windows Explorer

Firefox in the new profile should look like a factory fresh installation. Open the Troubleshooting Information page using either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• Help menu > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table, click the "Show Folder" button. Firefox will launch your brand new profile folder in Windows Explorer.

Leaving that folder open, switch back to Firefox, and Exit using either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

When Firefox closes, the profile folder should be front and center, or you can activate it using the Task bar.

Copy Old Data in Place of New

In that new profile folder you just popped open -- NOT the one on your desktop -- select all the contents (you can use Ctrl+a) and delete (you can press the Delete key on the keyboard).

Leaving that window open, open or switch over to your Old Firefox Data folder. Drill down into your old profile folder. At this level you should see a folder named bookmarkbackups among other things.

Select everything (Ctrl+a) and Copy (either right-click > Copy or Ctrl+c).

Switch to the empty new profile folder in other window and Paste (either right-click > Paste or Ctrl+v). This may take a minute since some of the files are large.

Start Firefox

Firefox should start up in that "new" profile with the resurrected old profile data. Success?

Thanks for your reply. >Could you check your desktop for a folder named Old Firefox Data?

There isn't one there and I also searched through all 3 of my external and internal harddisks and through my 4-disk Diskstation, nothing - neither a folder nor a file with that name was found, even just using Old Firefox, old firefox, firefox date, Firefox Data (so sometimes using capital letters or not). I have deinstalled the new version because I was also continuously getting the "Firefox cannot find the server..." message on umpteen websites although they opened perfectly well in my old Opera and in Chrome. I have re-installed 1.43 and have switched off auto-update. I have lost a days work and 10 hours because of this new update and to be honest I am furious. Reading through your certainly helpful reply if it had applied to me, I wonder why the backup system or whatever it is doesn't simply include a restore program so you can choose what you want to restore instead of having to go through all the steps you so helpfully included. My old settings are still on my laptop so I might try copying some files to a stick and pasting them into where they are on my PC. Might work...

The "Old Firefox Data" folder is ONLY used by the Refresh feature, so you would not expect to find it anywhere else.

When you installed Firefox 43, did it find your missing new tab data or color settings?

If not, is there anything else missing, such as bookmarks or add-ons?

Is your laptop "separate" that is, not connected with the XP system through Firefox Sync? If it is not currently connected, please don't connect it at this point.

OK, just to make things clear, I am talking about three different versions here: 1) My old Version, number unknown but from about December 2015 or so which worked fine, opened every website and which had my shortcuts on the New Tab page. These files were in my profile, some dating back to the end of 2015. 2) The 45.01 which I foolishly updated to at 14:00 hrs on Saturday. My folder then had new files dated 19.3.16 at ca. 14:00 hrs 3) The 43.01 which I re-installed after uninstalling 45.01 but the blasted thing keeps updating, even though I have selected "Never Check for Updates". It just started to again so I switched my router off as soon as I noticed, and told it to check for updates but ask me whether I want them or not. Many of the files in my profile are still dated 19.3.16 at ca. 14:00 hrs.

When you installed Firefox 43, did it find your missing new tab data or color settings? No, only stuff which had been put somewhere by the 45.0.1. update.

If not, is there anything else missing, such as bookmarks or add-ons? All my add-ons were missing after it updated to 45.01. My bookmarks appear to an old list. No new bookmarks which I had added since the beginning of the year are in the list.

Is your laptop "separate" that is, not connected with the XP system through Firefox Sync? If I can't even get Firefox to work properly, I'll be damned if I'm going to risk wrecking my laptop as well by using Sync !! (LOL) All I want is my shortcut startpage back, not any blasted "Mozilla Home Page" with a search, glaring white background etc. :-(

It is now 04:35 hrs Swiss time (that's gone 4:30 in the morning) and I'm going to stop trying to fix this - I'm off to bed !

Could you check for multiple profile folders? Windows hides Firefox's profile folders by default, so it's convenient to turn on viewing of hidden files and folders. This article has the steps: https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/win_fcab_show_file_extensions.mspx

Then drill down into:

C:\Documents and Settings\username\Application Data\Mozilla\Firefox\Profiles

If there is a second folder, that might contain your old data. Could you check the modification dates? Can you find a promising folder?

Unfortunately there is only one Profile listed, dated from yesterday 19.3.16. Instead of going to bed I checked the files in my HandyBackup backup folder (one set backups every night at 3 a.m. from C: to M:, the other backups once a week from M: to Z: ("data" on my Synology diskstation) but for some reasons I had never set it to backup my Firefox stuff), grrr.

Ah well, most of my tabs on the New Tab page are now back, but when I click on (x) to delete a shortcut, I have to press F5 to be able to get the "pin and (x) on the other shortcuts. I only had two or three add-ons anyway - a popup blocker (disappeared), the old New Tab (disappeared), an add-on which shows Greek letters when you use <font face="Symbol">... in html (disappeared), an add-on to change background colours etc. (disappeared)... I will download them again as I need them. Thankyou so much for your help and suggestions, but I think my Firefox is a hopeless case :-( </font>

Unfortunately, I can't explain what happened to your old profile folder if it's not in the regular Profiles folder or in an Old Firefox Data folder.

We occasionally see a glitch on newer versions of Windows after system updates where permissions or even user identity are confused and the system needs to be restarted to return to normal. I have never heard of that happening on Windows XP, however, and the days of system updates probably are behind us anyway.

Thanks anyway. I know I need a new computer, but my trusty old XP is so finely tuned to my needs - all my old programs (MS Office XP) work flawlessly, I can whizz through my work knowing where everything is and if anything needs tweaking, my XP and C++ allow me to do it. I have actually always had problems with Firefox, it either used to crash, or take a g e s to open a webpage, or suddenly refused to keep cookies (regardless of how many times I told it to keep cookies and even specified the pages for which it needed to keep them), orsuddenly disappear from my screen and from my "open programs" row at the bottom of my screen.... I don't have any viruses or trojans, so maybe Firefox just doesn't like me, haha... Thankyou so much for trying to help.

What security and cleanup software do you have?

I use the Pro version of AVG and the Windows firewall.