Could you check a few things:

(1) Shortcut hacked

The icon you use to start Firefox normally does not specify any particular website to load, but some external software will modify it and this will override your normal startup settings.

right-click the icon > Properties > Shortcut tab.

For 64-bit Windows, the "Target" should be no more and no less than the following:

"C:\Program Files (x86)\Mozilla Firefox\firefox.exe"

(2) Unwanted extension

Try disabling ALL nonessential or unrecognized extensions on the Add-ons page. Either:

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

In the left column, click Extensions. Then, if in doubt, disable (or remove, if possible).

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.

(3) user.js file

External software can create a settings override file. This article describes how to hunt it down if it exists: How to fix preferences that won't save.

Does that help?

I checked it all and no abnormalities. About your 3rd suggestion: my profile does not show a user.js file (which is strange since I remember fixing a similar issue with an unwanted toolbar in the past and remember something related to this. There was a screen with several files/lines and I edited one of them to get rid of the toolbar)

I have a lot of information so I really want to avoid to reset Mozilla... Can you help please?

By the way, thank you for your quick reply! :-)

Maybe this is a problem with session restoration restoring a pop-under windows.

How do you usually exit out of Firefox? I suggest using "Exit" from the classic File menu, or the "power" button on the new "3-bar" menu instead of closing windows or right-clicking the Task Bar button and using Close All Windows. Otherwise, you risk closing all the important windows first and having a pop-under window left as the one that gets restored.

If you are already doing that, it's possible that Firefox has lost the ability to update your session history file. This occasionally happens if the file is corrupted or locked. You typically can spot this issue by an accumulation of extra (numbered) sessionstore files.

To check on this, open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• Help menu > Troubleshooting Information

In the first table on the page, click the "Show Folder" button

Scroll down and look for files starting with sessionstore. If you see numbered files with a current date and time, e.g.,

sessionstore-1.js

then Firefox is not going to be able to restore your session normally because at startup, it does not look for those numbered files and instead just uses the old sessionstore.js.

If this is the issue - To resolve this, you probably need to remove the old sessionstore.js file and rename the latest numbered version. Here's how:

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

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

Pause while Firefox finishes its cleanup, then rename sessionstore.js to something like sessionstore.old

Rename the latest numbered sessionstore-#.js file to sessionstore.js

Start Firefox back up again. Any improvement in window/tab restoration?

No, but I found a solution by accident. I ran the adw_cleaner and there was a corrupt file in my firefox profile. I deleted it, restarted my computer and ever since it is all good.

Thank you again for your promptness and kindness. This forum is great for having specialists like you helping us. Thanks a lot!!

)