Sorry I did not reply but I am still experiencing difficulties with the FireFox Update page loading ion start-up.
Apparently this is a common fault and one of the solutions is to Type about:config in the address bar, click on the "I'll be careful" warning, look for browser startup homepage_override.mstone, double click, set to ignore.
or
Type about:config in the address bar, click on the "I'll be careful" warning, in the filter input field type start up, double click on browser start up.homepage override_url delete text string and click ok, close FireFox.
In both cases nothing happens when I "Double Click"