problems with internet explore

I have windows 8 on Dell Inspiron 14Z. Some days ago internet explorer started crashing. I installed Firefox; it worked for some time, but then it started crashing. I did a complete scan of the system with windows defender. No viruses or malware were found. I finally did a "system restore" and IE is now working. I shall appreciate any help as to the cause of the crashes, and on how to repair IE and Firefox.

I googled for IE repair but could not find any repair help for windows 8. .

Thanks.

Preet