There are different brands, sometimes do the same. The problem here is that some browsers read some tags and not others. If your browser can not read your codes, it will get your page to appear in a different way than what you intended. The trick is to write your code in such a way that all, or at least most browsers can read and display it like it is supposed to be.
You can find an HTML Tag List at: http://www.ncdesign.org/html/list.htm You can use this as you write your code and avoid some pitfalls. It includes only Netscape and Internet Explorer. These are the most used browsers, and probably includes about 80 percent or more of the online crowd.
You can check your html code by going to a validation service like Net Mechanic. You'll find a link to this and other validation services: http://marketing- resources.com/utilities.html This can be a humbling experience. It checks your code and give you all the errors and warnings.
Have your corrections, and check it again. You may have to do this a few times to end up with no errors.
There is no reason not to have absolutely clean HTML code. Getting tags and which browsers support them, and you're almost home. Then just run it through a validator. Now the world sees your page the way it really is.
