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1)uninstall firefox completely

2) Next run the cclener software and will clean any unwanted registries

http://www.filehippo.com/download_ccleaner/


3) Possibly you can run Malware bytes...

1)Try a system restore to earlier date where you didnt have any problem

2)uninstall Firefox and run ccleaner and hijack this and then reinstall Firefox again

3)Now try to change the router...

This behavior occurs if your user account does not have permissions to modify the Microsoft Windows Registry. Please follow the steps below to fix this issue.
Warning Serious problems might occur if...