The 'study' has apparently since been exposed as a hoax:
* BBC News: Internet Explorer story was bogus
> A story which suggested that users of Internet Explorer have a lower IQ than people who chose other browsers appears to have been an elaborate hoax.
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> A number of media organisations, including the BBC, reported on the research, put out by Canadian firm ApTiquant. (sic)
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> It later emerged that the company's website was only recently set up and staff images were copied from a legitimate business in Paris.
* IT News: Analysis: Is the Internet Explorer IQ test a fake?
> But whois records - the database that lists who was responsible for a website such as its technical contacts and owner - and web content comparisons raised questions over the company behind the survey that was the subject of the story.
So currently there is no evidence to support a link between IQ and browser choice
Other sources:
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