Don’t see a problem in FireFox, but here’s a thought:
Sidebars drop all the time in float-based (as opposed to table-based) themes if (for whatever reason) the two columns can’t fit side by side. Usually this happens if you put too wide of an image into a post, but it could also happen if you shrink the window down. This is especially a problem in IE. Search the forums for “sidebar drops” or something along those lines for ideas about what to do about it.
I saw what you are talking about. I often put a graphic up of the width I don’t want the page to shrink below when resizing the browser. If I design the page to look best at not less than 600 pixels, I put a 600 (+- a couple) image in to force the browser to start horizontal scrolling. I have made my top banner serve that function. There are probably other ways of doing this, but without using (argh!) tables, I don’t know of any, somebody else may be better equipped for a more elegant solution.
its a fluid width design. the content width is set to 100% if you dont want your content to move around when the window is resized, give it a fixed width, like 800px or 900px or 1000px, whatever you prefer. youll find the setting in your stylesheet