hello pjagota, are there any crash reports showing up, that you could provide?

1. Enter about:crashes in the Firefox location bar (that's where you enter your website names) and press Enter. You should now see a list of submitted crash reports.
2. Copy the most recent 5 report IDs that you see in the crash report window and paste them into your forum response.

Hi philipp thanks for your response , there is no crash reports available in about:crashes and further the same problem is occurring while I try to download any file.

Thanks & Regards

i've seen the exact same symptoms in this question: https://support.mozilla.org/en-US/que.../944111 (unfortunately no solution has been found...

please try to run a full scan of your system with the security software already in place and different tools like the free version of malwarebytes, adwcleaner, microsoft safety scanner & kaspersky security scan.

Hello try from command line start > run the next:

"C:\Program Files\Mozilla Firefox\firefox.exe" -preferences

and check if works

thank you

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox