Last time I tried to look at Glassdoor it just required you to provide information to get information. Once you provided a salary, you could access salaries for a year.
Incidentally, if you really want you can get around this by opening a new incognito window in chrome. Sort of a pain and perhaps not worth the effort, however.
I run a similar site to Glassdoor that doesn't require you to write a review to read them. Understandably, I have fewer reviews, but if you're interested feel free to take a look!