Q:

jQuery problem with firefox, isn't it cross-browser compatiable?

I have problem here with this code below it works on all browsers except Firefox ,it's in external js file and the link in aspx file
$(document).ready(function () {
    var h = $(".img_cover").width() ;
    if ($.browser.msie) {
    $(".download_box").width(h + 1);
    $(".download_pdf").width(h + 1);
    $(".right_column").width(h);}
    else{
    $(".download_box").width(h - 22);
    $(".download_pdf").width(h - 22);  
    }
 });

Issue details:

there is an image of a magazine and there is a download button below it
those magazine images come in different sizes, so adjusting the width of the download 
button below that image to match the width is necessary
I wrote this jquery code to do this automatically.. 

Testing:
Local: works fine on all browsers 
Web Server: (externally linked to ASPX master)

Firefox: jquery code not initialized
Explorer 6/7/8: works fine
Opera: works fine

Code in the generated aspx
<!DOCTYPE html PUBLIC "-//W3C//DTD MathML 2.0//EN" "http://www.w3.org/Math/DTD/mathml2/mathml2.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:mml="http://www.w3.org/1998/Math/MathML">

<head id="ctl00_Header">
<title>Abstract and Applied Analysis — An Open Access Journal</title>
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<script src="http://beta.source/Scripts/JQInt.js" type="text/javascript"></script>

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<meta content="Abstract and Applied Analysis is a mathematical journal devoted exclusively to the publication of high-quality research papers in the fields of abstract and applied analysis. Emphasis is placed on important developments in classical analysis, linear and nonlinear functional analysis, ordinary and partial differential equations, optimization theory, and control theory. Abstract and Applied Analysis supports the publication of original material involving the complete solution of significant problems in the above disciplines. Abstract and Applied Analysis also encourages the publication of timely and thorough survey articles on current trends in the theory and applications of analysis." name="Description" />
<link href="/journals/aaa/rss.xml" rel="alternate" title="Abstract and Applied Analysis latest articles" type="application/rss+xml" />
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                        PDF Download (1.7MB)</a> </div>
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                <h2>Topological and variational methods of nonlinear analysis and 
                their applications</h2>
                <span class="press_info">Guest Editors: V. G. Zvyagin, Yu. E. Gliklikh, 
                V. V. Obukhovskii, A. I. Perov, B. N. Sadovskii, Yu. I. Sapronov, 
                V. A. Sobolev, and Z. B. Tsaliuk</span>
                <ul class="more_articles_ul">
                    <li><a href="/journals/aaa/2006/093926.abs.html">Topological 
                    and variational methods of nonlinear analysis and their applications</a>, 
                    V. G. Zvyagin, Yu. E. Gliklikh, and V. V. Obukhovskii<br />
                    Volume 2006 (2006), Article ID 93926, 2 pages</li>
                    <li><a href="/journals/aaa/2006/036215.abs.html">The Kolmogorov 
                    equation in the stochastic fragmentation theory and branching 
                    processes with infinite collection of particle types</a>, R. 
                    Ye. Brodskii and Yu. P. Virchenko<br />
                    Volume 2006 (2006), Article ID 36215, 10 pages</li>
                    <li><a href="/journals/aaa/2006/039786.abs.html">Necessary and 
                    sufficient conditions for global-in-time existence of solutions 
                    of ordinary, stochastic, and parabolic differential equations</a>, 
                    Yuri E. Gliklikh<br />
                    Volume 2006 (2006), Article ID 39786, 17 pages</li>
                    <li><a href="/journals/aaa/2006/086173.abs.html">On calculation 
                    of the relative index of a fixed point in the nondegenerate 
                    case</a>, A. V. Guminskaya and P. P. Zabreiko<br />
                    Volume 2006 (2006), Article ID 86173, 11 pages</li>
                    <li><a href="/journals/aaa/2006/082602.abs.html">Theorem on 
                    the union of two topologically flat cells of codimension 1 in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>
                    ℝ</mml:mi><mml:mi>n</mml:mi></mml:msup></mml:mrow></mml:math></a>, 
                    A. V. Chernavsky<br />
                    Volume 2006 (2006), Article ID 82602, 9 pages</li>
                    <li><a href="/journals/aaa/2006/078928.abs.html">Bourgin-Yang-type 
                    theorem for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>
                    a</mml:mi></mml:math>-compact perturbations of closed operators. 
                    Part I. The case of index theories with dimension property</a>, 
                    Sergey A. Antonyan, Zalman I. Balanov, and Boris D. Gel'man<br />
                    Volume 2006 (2006), Article ID 78928, 13 pages</li>
                    <li><a href="/journals/aaa/2006/048132.abs.html">Gantmacher-Kreĭn 
                    theorem for 2 nonnegative operators in spaces of functions</a>, 
                    O. Y. Kushel and P. P. Zabreiko<br />
                    Volume 2006 (2006), Article ID 48132, 15 pages</li>
                    <li><a href="/journals/aaa/2006/051794.abs.html">An oriented 
                    coincidence index for nonlinear Fredholm inclusions with nonconvex-valued 
                    perturbations</a>, Valeri Obukhovskii, Pietro Zecca, and Victor 
                    Zvyagin<br />
                    Volume 2006 (2006), Article ID 51794, 21 pages</li>
                    <li><a href="/journals/aaa/2006/043560.abs.html">Flow of electrorheological 
                    fluid under conditions of slip on the boundary</a>, R. H. W. 
                    Hoppe, M. Y. Kuzmin, W. G. Litvinov, and V. G. Zvyagin<br />
                    Volume 2006 (2006), Article ID 43560, 14 pages</li>
                    <li><a href="/journals/aaa/2006/056367.abs.html">The integral 
                    limit theorem in the first passage problem for sums of independent 
                    nonnegative lattice variables</a>, Yuri P. Virchenko and M. 
                    I. Yastrubenko<br />
                    Volume 2006 (2006), Article ID 56367, 12 pages</li>
                    <li><a href="/journals/aaa/2006/094509.abs.html">On a certain 
                    functional equation in the algebra of polynomials with complex 
                    coefficients</a>, E. Muhamadiev<br />
                    Volume 2006 (2006), Article ID 94509, 15 pages</li>
                    <li><a href="/journals/aaa/2006/090837.abs.html">The mappings 
                    of degree 1</a>, Maria N. Krein<br />
                    Volume 2006 (2006), Article ID 90837, 14 pages</li>
                    <li><a href="/journals/aaa/2006/098081.abs.html">Surgery and 
                    the relative index in elliptic theory</a>, V. E. Nazaikinskii 
                    and B. Yu. Sternin<br />
                    Volume 2006 (2006), Article ID 98081, 16 pages</li>
                </ul>
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This 
is the jquery link 
<script src="http://beta.source/Scripts/JQInt.js" type="text/javascript"></script>

A:

jQuery is cross-browser compatible. The problem is more likely to be in your code than in the jQuery source, so that would be the first place to look.
The first thing that stands out is the use of browser-detection code. jQuery recommends use of $.support instead of attempting to tailor code to specific browser versions, as your code will be more flexible going forward.
Secondly, what is the behaviour that you expect to see, what do you see in IE et.al and what do you see in Firefox? Having a clearer picture of your expectations is likely to lead more quickly to the correct answer.
EDIT:
Here's a Working Demo using your code, that works for me in Firefox 3.5.3. Add /edit to the URL to see the code. As can be seen, all <div> elements are set to be width 100px. When the DOM has finished loading, the width of <div class="download_box"> and <div class="download_pdf"> is shortened by 22px in all browsers other than IE.
jQuery code
$(document).ready(function () {

    var marker = $('#browser');
    $.each($.browser, function(i, val) {
      $("<div>" + i + " : <span>" + val + "</span>")
                .appendTo(marker);
    });

    var h = $(".img_cover").width();

    if ($.browser.msie) {
    $(".download_box").width(h + 1);
    $(".download_pdf").width(h + 1);
    $(".right_column").width(h);
    }
    else{
    $(".download_box").width(h - 22);
    $(".download_pdf").width(h - 22);  
    }
 });

relevant HTML
  <div class="img_cover" style="width:100px;background-color:blue;">.img_cover</div>
  <div class="download_box" style="width:100px;background-color:blue;">.download_box</div>
  <div class="download_pdf" style="width:100px;background-color:blue;">.download_pdf</div>
  <div class="right_column" style="width:100px;background-color:blue;">.right_column</div>
  <br/>
  <div id="browser"></div>

