I have laptop, couple of months old, running W7. I've been happily using Firefox as my default browser all that time (and for years before on other computers) and this morning, I wake up and boot up and Firefox won't open. I have run virus checks, with Avast: File.exe, which has been "locked in a chest". Also ran a malware check with Malwarebytes, and also ran CCleaner on everything. Uninstalled then reinstalled and still nothing. I just cannot ge the thing to run.