By the way, a 37.0.1 update was released today to address some severe startup crash issues, so you might try installing that before doing more troubleshooting.

If using Help > About Firefox does not retrieve the update, you can get a full installer from this page (scroll down to your preferred language):

https://www.mozilla.org/firefox/all/

You don't need to uninstall Firefox before running the new installer.

When Firefox crashes, it usually records information about what was happening at that moment. If you have seen the Mozilla Crash Reporter, then almost certainly there is some data there which could help in troubleshooting. Please check the last section of the support article "Firefox Crashes" for steps to get the report IDs for the crashes you submitted, and then post some of the recent ones here.

If necessary to use the about:crashes screen, you might try starting up in Firefox's Safe Mode. (That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.)

If Firefox is not running: Hold down the Shift key when double-clicking the Firefox shortcut/icon.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

Not all add-ons are disabled: Flash and other plugins still run. OK the restart when asked to confirm.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Thank you for the extra info:

Report-ID (Meldungs-ID): bp-6b25134a-5840-49da-8f9f-e3e862150403

This crash is somewhat mysterious and I don't think we have enough information to know the cause.

Did Firefox also crash in Safe Mode or was it able to start and run more normally?

I installed the 37.0.1 update, but Firefox still crashes and it also crashes in Safe Mode.

I think that the crash report is about Cycle Collection to cleanup unused JavaScript data.

Do a malware check with several malware scanning programs on the Windows computer. Please scan with all programs because each program detects different malware. All these programs have free versions.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender:
  http://windows.microsoft.com/en-us/windows/using-defender
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked
• https://support.mozilla.org/kb/troubleshoot-firefox-issues-caused-malware

Do a clean reinstall and delete the Firefox program folder before (re)installing a fresh copy of the current Firefox release.

• Download the Firefox installer and save the file to the desktop
  https://www.mozilla.org/en-US/firefox/all/

If possible uninstall your current Firefox version to cleanup the Windows registry and settings in security software.

• Do NOT remove "personal data" when you uninstall your current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including data in profiles created by other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
• (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other personal data are stored in the Firefox profile folder and won't be affected by an uninstall and (re)install, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

If you keep having problems then also create a new profile.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

I have now used every of that programs and none found something worse than tracking cookies, which they removed. I also did a clean reinstall, but my Firefox still keeps crashing.