Hi Tim, My first guess is that you have a malware problem. For future reference note that you should normally not need to delete the ''AddData''. You are likely to use important profile data by taking that course of action. If problems arise in the profile the usual solution is to create a new profile after backing up the original files. (I realise you mention Profile Manger and may already have attempted that.) To do a clean install what you need to remove are the files in the Program path. * http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall ---------------- For reference *Your report for CrashID[[https://crash-stats.mozilla.com/report/index/92ce0158-863a-4068-9ae9-076852120310 92ce0158-863a-4068-9ae9-076852120310] **Signature: mozalloc_abort(char const* const) | _RTC_Terminate | PK11_InitSlot ** no associated bugs ---------- Possibly you have a malware problem. I note an undated/unversioned library file (''logevmin.dll'' ) is showing up in the above report (ignore mozjs.dll that is normally undated) anything with no date is at first glance suspicious and warrants further investigation as possibly it could be a corrupt or infected file, or malware masquerading as something else. * see [[is my firefox problem a result of malware]] * and typical advice [/questions/914980#answer-302372] It may also be worth trying Windows own Safe Mode (accessible usually by use of the keyboard F8 key) it may be a diagnostic step that prevents the startup crash.