Firstly, your English is quite good so don't worry about that

To fix your issue, try to re-download the installation file from https://www.mozilla.org/en-GB/firefox/new/ Uninstall the currently installed firefox and try to install firefox from the latest installer

If this does not work which sounds plausible try this solution to a similar problem:

"" The item that may be the cause is indicated by the Bitdefender agent. I would recommend you add the TB profile folder as an exclusion in BD (https://www.bitdefender.com/support/adding-exclusions-in-bitdefender-2094.html) and see if TB runs OK in Windows normal mode. The default location of the profile on Windows is:

C:\Users\<winusername>\AppData\Roaming\Thunderbird\Profiles\<8charstring>.default

AppData is a hidden folder (https://support.microsoft.com/en-us/windows/show-hidden-files-0320fe58-0117-fd59-6851-9b7f9840fdb2), by default.

RapportService is also a security program promoted by banks, but I don't think it has any effect on email.

Safe mode also loads basic drivers for e.g. graphics and touchpad, but I doubt yours have changed for years. Bitdefender is the first thing to look at. ""

This is the original thread and it has some more information on it if you need some extra help:

https://support.mozilla.org/en-US/questions/1271536#answer-1261669

If the above does not work, Let’s do a full clean re-install;

Note: Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

Download Firefox For All languages And Systems {web link}

Firefox ESR; Extended Support Release {web link}

Beta, Developer, Nightly versions https://www.mozilla.org/en-US/firefox/channel/desktop/

Install Older Version Of Firefox {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

How to Start all Computers in Safe Mode; {web link} Free Online Encyclopedia