Dude, your web site is crap.
How did this happen? You think it looks great.
Frequently, this happens when you design and test your blog for one browser, and your friend uses another. Firefox and Internet Explorer, which use differing code and display standards, are famous for this problem.
Back when the web was young, both Microsoft (developer of Internet Explorer) and Mozilla (developer of Firefox) were members of the WWW Consortium (W3C). One of the tasks of W3C was to develop standards - to say
For this code, this is how it shall be displayed.
Microsoft and Mozilla agreed to standards - which they may or may not support.
Both Microsoft and Mozilla signed off on standards, to make their browsers compatible. Web code (HTML) is supposed to be browser independent. Anything that works in Firefox should work in Internet Explorer, and vice versa.
But Microsoft signed off on the standards, then turned around, wrote Internet Explorer, and ignored those standards. There are significant differences between the way Firefox (standard) and Internet Explorer (non-standard) render HTML. Note that IE V7 appears to be more standards compliant in its rendering.
You need to test any changes, in multiple browsers, for reliable changes.
And that's why blogs (and web sites) written to look good in Internet Explorer may look like crap in Firefox. The bottom line? You have to test your blog, in both browsers, and in all major browser versions, when you make changes.
When you test, use common sense. Don't put things (pictures for instance) in places where they don't fit. Check the width of any graphics, before positioning them.
Use online services, to test multiple browsers at different version levels.
Fortunately, you don't have to have banks of computers, to test all of the possibilities. Free online browser display services, such as AnyBrowser or maybe BrowserShots, will simulate your blog on different browsers. And W3Schools Online Web Tutorials will provide in depth research.
Occasionally examining appearance, at differing zoom levels, may be a good idea. Don't wait for older (or younger) readers to complain.