I'm not sure where those updates are coming from, but in addition to program updates, Firefox does various add-on updates at startup. Perhaps one of your add-ons has a bad update??

Firefox's Safe Mode is useful for diagnosing add-on issues. You might want to first make a backup of your Firefox profile folder. This article can help you locate it: Profiles.

This article describes how to use Firefox's Safe Mode. Be careful not to "reset" anything permanently if you didn't back up.

If you can browse normally in Safe Mode, you might try disabling your add-ons and then gradually bringing them back as needed.

If Safe Mode has the same problems, some external software might be to blame. You may want to run some supplemental scans. These two tools are highly regarded:

Malwarebytes Anti-malware : http://www.malwarebytes.org/products/malwarebytes_free

SUPERAntiSpyware : http://www.superantispyware.com/

I wouldn't trust such a file.

Did you try to test it with your anti-virus software or with an online scanner?

• http://vms.drweb.com/online/?lng=en Dr.Web - innovation IT-security solutions. Complex protection against Internet threats.
• http://www.eset.com/onlinescan/ - Free ESET Online Antivirus Scanner
• http://www.kaspersky.com/kos/eng/partner/default/pages/default/check.html?n=1246229256418 - Kaspersky Online Scanner

--- You may have Firefox open a tab that downloads that file.

You can try to clear the download history and maybe delete sessionstore.js in the Firefox profile folder as well in case Firefox tries to recover a session that crashed or wasn't closed properly.

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

If I would just uninstall and reinstall firefox? Would it help? Clean install and everything, and just re-install each plugin manually.