Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

That did'nt solve the problem

There is no need to run the all.js (mozilla firefox\greprefs\all.js - resource:///greprefs/all.js) file. It is a Firefox JavaScript file that stores some default prefs and the Windows JScript program doesn't handle that file. You would normally only get that error if you double click the file.

thanks for that