I have read other Q&A related to same issue. Following auto-update of Firefox on 22nd Oct. I cannot open Firefox. I have tried the recommended solutions to install a clean version of Firefox both by renaming the Firefox folders and completely deleting them. No change. I have run Malwarebyte and run a system scan with no faults found. I can continue to use MS Edge. Chrome does also not open which would suggest a setting issue or something causing a start up process corruption. I noted other reports that some applications can cause the problems. I do not use Zonealarm. I have removed recently installed apps. including Dropbox. Both Firefox and Chrome work when pc restarted in Safe mode. I've checked Win Event Viewer and can find the error record for Firefox (& Chrome). Faulting application name: firefox.exe, version: 56.0.1.6484, time stamp: 0x59d2c74f Faulting module name: ACCELE~2.DLL, version: 0.0.0.0, time stamp: 0x52f04604 Exception code: 0xc0000005 Fault offset: 0x0000000000118a13 Faulting process id: 0x2150 Faulting application start time: 0x01d34d001282c11e Faulting application path: C:\Program Files\Mozilla Firefox\firefox.exe Faulting module path: C:\PROGRA~3\ACCELE~1\ACCELE~2.DLL Report Id: 86e8eb3c-3b4a-4296-857e-810bf54865b0 Faulting package full name: Faulting package-relative application ID: I've now run out of ideas for fixes. Any ideas, please??