Try to drag the old version to the trash.

• http://kb.mozillazine.org/Uninstalling_Firefox

Thank you, but it did not work. I always get the message that I can not open the new one because one is 'open'. Now all my firefox programs are in the dustbin but still there is one 'open'. How?

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

See Basic Troubleshooting: Make a new profile:

• https://support.mozilla.com/kb/Basic+Troubleshooting#w_8-make-a-new-profile

If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files)

See:

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

Thanks, I tried a lot of your things and now it works!