hello isatinov,

follow the steps:

Chosen Solution

Hello,

The Refresh feature (called "Reset" in older Firefox versions) can fix many issues by restoring Firefox to its factory default state while saving your bookmarks, history, passwords, cookies, and other essential information.

Note: When you use this feature, you will lose any extensions, toolbar customizations, and some preferences. See the Refresh Firefox - reset add-ons and settings article for more information.

To Refresh Firefox:

  1) Open the Troubleshooting Information page using one of these methods:

• Click the menu button New Fx Menu
• Click help Help and select Troubleshooting Information.
• A new tab containing your troubleshooting information should open.

If you're unable to access the Help menu:

type about:support in your address bar to bring up the Troubleshooting Information page.

  2) At the top right corner of the page, you should see a button that says "Refresh Firefox" ("Reset Firefox" in older Firefox versions). Click on it.

   3 Firefox will close. After the refresh process is completed, Firefox will show a window with the information that is imported.

  4  Click Finish and Firefox will reopen. 

Did this fix the problem? Please report back to us!

Thank you And Regards,

Arman

Thank you.

Hi isatinov, if you check your history, can you track down the instructions you followed?

If one of those deleted your history, then I guess that wouldn't work...

By any change did you turn on privacy.resistFingerprinting preference in the about:config preferences editor? That has some effect on window sizes and zoom levels, although I don't recall the full details (I don't use that setting myself). You may want to make sure that is set to false here:

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

(2) In the search box in the page, type or paste finger and pause while the list is filtered

(3) If the privacy.resistFingerprinting preference is bolded and has a value of true, double-click it to restore the default value of false

More info on about:config: Configuration Editor for Firefox.

Are you possibly using Resist Fingerprinting?

• https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting

You can check this pref on the about:config page to see if Resist Fingerprinting is enabled and if this pref is user set (bold) reset to false via the right-click context menu.

• privacy.resistFingerprinting = false

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Thanks to all. Problem solved. It was the Resist Fingerprinting set to true that forced Firefox to open as a set shape and position window. Setting to false has Firefox opening in full screen.