I was at the local library looking at a website I built and what was showing up seemed to be a scrunched version of what I made. On my computer, in Firefox and IE (with 1024 and 800 screen sizes), and on a friend's computer, the site looked fine. However on the library's computer (screen: 800x600) the main body of text was scrunched and flowing into the boxes on the right. And it seems the boxes on the right had expanded in width.
I built the boxes in a floating table (because I couldn't get the css to place the boxes where I wanted) and the table is 250px wide. The main text is 100% or whatevers left over.
It actually looked okay to me in Firefox 188.8.131.52, but I checked the validation, -42 'warnings'.
You got two "<head>" and two "<body>"s, deprecated and proprietary ("old" and "IE-only") code, no !doctype statement (this alone could account for any problems in IE, which is now in 'quirks mode' because it doesn't know what to do without proper !doctype)... See screenshot image for partial list of errors.
Get Firefox the browser, and next get "HTML-Validator by TIDY", the extention. Install it, run it. It has a 'clean up the code' button which, if there are no ERRORS, will correct all WARNINGS (which are 'error-lites', really, but potentially page-busting at that), and present you with 'cleaned code' to copy & paste back as the document.
This might however, make the document not look right in browsers... in which case, then, fixing it properly can ensue.
Until the 'warnings' are corrected, there really isn't any way to 'fix' the cross-browser differences that you cite.