If you actually read the linked article, it has measurements for how much RAM strings use in Gmail. For the particular case of the article's author, it was abo

If you actually read the linked article, it has measurements for how much RAM strings use in Gmail. For the particular case of the article's author, it was about 11MB of strings before the changes he made; it was about 6-7MB of strings afterward. Your mileage will vary depending on what actual mails you have, of course. Note also that comparing this to the Chrome numbers for overall Gmail memory usage is comparing apples and oranges: Firefox tends to use less memory than Chrome. You'd want to look at about:memory in Firefox to see how much memory that gmail page is likely using.