Another tool I often recommend besides AdwCleaner(Adaware Cleaner) is JRT(Junk Removal Tool) also available through Bleeping Computers. Both are effective in removing browser hijacks. And are portable apps that do not require install. You can run them from your desktop.
To answer your earlier question regarding Firefox. In most cases, you don't have to re-install Firefox for these types of issues. In fact, re-installing Firefox without removing your existing profile, doesn't remove the problem.
The easiest way is to just create a new Firefox profile which can be done by:
- Hold down Windows Key+R and in RUN, type Firefox -p and press ENTER key.
- Click the Create Profile button, and follow the prompts.
- Make sure the option to automatically start Firefox with your new profile is checkmarked.
You're now running Firefox as if it were just installed. In which case, you'll have to import any bookmarks and install any extensions you previously were using.