If that doesn't work, try AdwCleaner. Some of these programs (eg: Malwarebytes, AdwCleaner) have their own special areas of expertise in rooting out adware, and they don't fully duplicate each other.

Also, examine the shortcuts you use to start your browser(s). Look at their command lines (right-click the shortcut > Properties > Target box) to see if anything has been added to the trailing end of the normal command that should start the browser. If there is, delete that extra material (usually a URL) added by the adware.

Finally, realize that if Malwarebytes indeed found "lots of threats", you may be dealing with a badly infected system, including rootkits and self-hiding viruses. Certain of these things invite all their friends to come join them on your computer, and the more trash that is on the system, the more the chance for a truly deep infection. If that turns out to be the case, you may need to ask for "guru" help at a reputable malware-removal website (like Wilders, Malwarebytes, DSLR, etc) in order to do all the things necessary to dig out whatever is going on.