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How to debug web page rendering compatibility issues across browsers?

I am developing a web page primarily using Firefox. Often I encounter that my web page renders properly in Firefox but has some unexpected behavior in Chrome and IE.
Generally if its related to javascript, I usually open Developer Console in Chrome and see if there were any errors and that gives me a clue as to what might be wrong.
Unfortunately, I am generally lost if its a CSS related or HTML element issue.
In one particular case, I have placed a div inside a <td> and I am lost as to why the chrome cannot render it properly irrespective of the fact that firefox is happy and does not complain.
So my question is, how to debug issues related to rendering of HTML pages in Chrome and CSS and determine what might be offending.
My related question is, is there a guidelines to make my web page work in almost all the popular browsers with little effort? I am particularly thinking in terms of tool or process which will warn me of compatibility issues with my web page.

IE (Internet Explorer) and little effort doesn't match to each other, you have to invest more of your time and effort only for IE, illuminate IE and be happy, as a suggestion, use Twitter Bootstrap if possible, it's a ready and tested css framework (maybe framework is not perfect name).
Basically, as far as I know, only a css reset could be used to gain some consistency but still you have to test over different browsers because each has different rendering engine. If you want to keep IE in the list then test the layout for IE at first.
Only for the IE or Inconsistent Exposer (IMO) there is a developer tool available (IE Tester) to test layout (HTML/CSS) over different versions of IE and only works on Windows so it may help you a bit if you are Windows user. There is also an online tester available and sometimes helpful, it's browsershots.org.
Also IE has a debugger/developer tool and pressing F12 will bring it so you may see something like this:
Google Chrome has it's built in debugger/inspector (CTRL + SHIFT + I) and on Firefox you may use Firebug extension and these browsers are not dumb like IE and there are lots of debugging extensions available for these browsers for free, not worried about these good guys.
Generally speaking, IE users are dumb and used to see dumb things on their screen so I don't think too much about them because they really don't know the difference but as a developer you may need to think about it and in this case I would demand extra charge from my clients if they want me to make a site compatible for IE < 10 because it requires extra effort.
You dunno me ? Leh--hoo-zehar (Looser) IE am a legendhhh. Smooky...!

I am not aware of any tool that will warn you because there is no way for a tool to validate the result of what you desire.
As far as how to test HTML/CSS. Chrome supports the most HTML-5 and FF is a close second. If you develop in chrome it normally works in FF and via verse. IE is where the pain is. IE does not support all HTML tags and often will render things wonky. I normally create my webpage and focus on FF and chrome once I like the results I open IE and debug. 98% of the time it is CSS changes that need to be made. I debug CSS first and if I am not able to resolve it with CSS after a decent amount of work I will look into changing the HTML. I try to avoid changing HTML because you have to debug all other browsers again.

Styles and code developed in Chrome will generally work in Safari, Opera(same engine), and IE 10+ with few inconsistencies. You'll get a few rare positioning issues with some CSS3 specs in Firefox, specifically in background positioning. You'll also find some javascript issues unique to Firefox.
IE9 is generally a good sport and usually doesn't have too many issues. IE8 will have a few and they'll be significantly different based on the OS (as there are multiple versions of each IE and they all support different specs for Javascript and HTML) specifically you'll find lots of issues with XP IE8 and really shouldn't support it (Microsoft doesn't even want to).
For the most part you'll be developing to IE inconsistencies unless it's a CSS3 spec with the occasional javascript strangeness (which js frameworks generally can help with since a few of them were made with that goal in mind).
As far as tools, browserstack is nice but doesn't give you a lot of time. If what you're trying to use is modern caniuse is a good place to visit first. Almost all issues between non-IE browsers will be HTML5 or CSS3 specific though.

Cons of using Internet Explorer's Compatibility Mode

What are cons of force a web site viewed in IE to compatible mode? Say we force IE9 to IE8 compatiblity mode?
Performance drawbacks
Can't use any new IE9 specific features like HTML5/CSS3/SVG
Why?
We run legacy web app which is developed since 2000 so it's a mess ball fighting to be compatible with Chrome, Opera, Firefox, IE6/7/8 and now we decide to add IE9 to the list. But with IE9 we run in issues with printing, "Permission deniend" JavaScript errors (probably something about cross-frame JavaScript calls) and next issues - the easy workaround is to force IE9 to behave as a IE8 and then everything works fine. But I am still not sure if it's way to go...

first our app is public site (for our clients)
You have a public website developed in 2000 and it doesn't work on modern browsers? Deprecate it or re-write it.
Don't hack your code to support modern browsers, the website is clearly poorly written and doesn't apply to standards. You can't get away with this.
The only place where you can get away with this level of incompatibility is intranet applications and even then you should simply state "it works on browser X, live with it"
You can't say that to public facing clients. I mean you can try, but have fun losing business to your competitors.
Re-develop your website to match the W3C HTML/CSS standards and the ES5 standards and it will be completely future facing (for some years).
Alas, the way the web works is that anything more then 5 years old is deprecated. So either re-write it every 5 years or get out of the web business.
In terms of actually using compatibility mode, don't. IE6-8 are horrible engines and should be avoided like the plague. If you use them then you can't write future facing standards compliant code.
Your code needs to match the standards and you should fix / shim / patch any browser specific bugs where those browsers don't implement the standards.

You cannot say you have tested in IE6/7/8/9 until you have tested in those different versions. Emulating the test environment is not the same as using the test environment. To my knowledge IE7/8 compatibility modes are the older render engines, not the underlying browser as a whole, bugs and all. It is closed source so you will never know.
Convert Microsoft's free to download virtual disk images for cross-browser testing to Virtualbox images and put them on a machine that just runs Virtualbox. An old machine will do, run the VMs headless and access them with remote desktop. In that way you will be able to test in all browsers without burdening your machine with MS/Spyware.

I believe your system admins can set IE to compatibility mode for all intranet traffic using the Group Policy Editor. Any site you create will from this point forward, you can add a meta tag to force IE9 to render natively and use all the newer features...
I'm having to do that on my current project using the following doctype and meta tag in my header:
<!DOCTYPE HTML >
<meta http-equiv="X-UA-Compatible" content="IE=100" />

Compatability mode is something that MS introduced to give people some chance to upgrade their applications, not for long term use. AFAIU.
If you want your application to be compatible with IE9, then you will have to change it. If you are trying to maintain IE6-9 compatibility then you have a real challenge, and you should consider whether this is really practical - in essence, you need at least 2 distinct sets of html. Is this practical for you?
IE9 compatibility mode is different form IE9 and IE8 - it draws bits from both. So you need to do a full test agaisnt the compatibility mode version, and ensure that it remains working against this.
So in answer to the question, the cons are that you are not being IE9 compatible, and there is a danger that when IE10 comes out, your code will not run against that in any mode. You are putting the effort into compatibilty testing without providing for future changes. You would do better, in the longer term, to make your code IE9 compatible. Also, the message you are giving your clients is that your code base is not going to be compatible for much longer. Unless you are talking to them about a re-work, this is a real negative.
However, it sounds like your entire code needs a re-work, to forget about IE6 and be written for modern working browsers. Using compatibility mode until that happens is probably OK. If you do this - and tell your clients - then staying in compatibility mode is viable.

Using compatibility mode will NOT cause the browser to use the JavaScript engine that was present in the old version of IE.
By that I mean it will run any JavaScript code using the IE9 engine. Which was a problem for us when debugging an old product that had a problem with IE7/8.

How to debug Javascript on old browsers

Forgive me if this has been asked elsewhere. I was not able to find a good answer yet. I have some Javascript code that works perfect in the latest release of Firefox. However, there is some odd behavior on an older browser that is used on our site. For reasons beyond my control, I need to support this hacked up version of a browser that is actually embedded into another piece of software.
I am stabbing in the dark as to the cause of the issues. I see no error console and of course tools like Firebug are a pipe dream. How do I effectively debug browser-specific issues? The old guess-and-check method will cost way too much time.

You can use Firebug Lite in IE6+ and older versions of FF/Opera/Webkit. The most useful feature of Firebug Lite in my opinion is probably the logging capabilities (console.log).
Checking the JavaScript for syntax errors before you even load the page with a tool like JSLint can save you some headaches. As a last resort, the reliable window.alert is always there.

It depends on the browser.
You may want to look at Firebug Lite for Firebug-like features in older and non-Mozilla browsers.
If the browser is weird enough that you really have to guess and check on the client side, I'd recommend writing a pretty good set of tests to run on every browser.

good luck with alert()'s
but you can try :
1) IE8 has the developer tools, that works fine in compatibility mode.
2) Firebug lite http://getfirebug.com/firebuglite#Stable
3) charge more from your damn clients that wants the thing to work in IE6

If you can make do with logging, my own logging library log4javascript works in every major browser released since 1999.

Browser Independent JavaScript debugger?

Does anyone know if a browser-independent debugger exists...
For example I have been using Firebug in Firefox but if the web developers use other browsers - nothing.
I was wondering if there is some kind of "global" debugger that can attach to any browser and just debug?
Any ideas?

The makers of Firebug also make Firebug Lite, a JavaScript file that you can include in your webpage. They say that it works in IE, Opera, and Safari.
Steve

Since each browser has its own engine with its own quirks and such, it's more or less impossible to have a universal debugger.
Aptana, which is really just a rebranded Eclipse for web projects, has a debugger built in to the IDE, and comes closes to that ideal--in theory. It uses the Eclipse platform's debugging interface, but it still needs to be plugged into a browser. In Firefox, this works by plugging into...Firebug's JS debugger. But, it allows you to set breakpoints and step through code directly from the IDE (quite helpful for external JS files). For IE debugging, you need to purchase the Pro version, so I can't vouch for its quality. AFAIK, it doesn't support other browsers.

Nearly all the browsers have there own JavaScript debugger. Simply because they don't provide the same API (if they provide some) for accessing the JavaScript engine.
So, to complete your list, you have DragonFly for Opera, and WebInspector for the browsers based on WebKit (like Safari).

For IE you can also use Visual Studio to debug JavaScript - and it's better than the Microsoft Script Debugger. I'm not sure if the express editions are also capable of this.
Added: Both VS2005 and VS2008 are capable of JS debugging, although the newer product is better of course.

I run a Webservice that allows developers to "debug" their Javascript in the sense of finding bugs via a Javascript validator. See the HTML5 IDE guide for details to set it up with the "global" vim editor.

You can debug javascript with express edition of visual studio. Look here for details

Short answer: I don't believe so, but I hope you find one because I'd love to have one.
However, if you haven't been following IE development lately, IE's JScript debugging is alot less painful now with IE8; it includes, by default, some dev tools that do pretty much everything that Firebug does with the exception of AJAX debugging (but I prefer a protocol analyzer anyways for AJAX). It even implements an executable console, which includes several of the console.X methods from Firebug!
The profiler, I'm tempted to say, is nicer than Firebug's - simply because it lets you export the results directly to CSV. The actual debugger is as full-featured as JS debuggers get, with stepping/breakpoints/direct input.
Also, I haven't heard Venkman mentioned yet; its the grand-daddy of Firefox debugging (and other Mozilla Javascript). Not as popular as Firebug, but it definitely has its followers.
Lots of good information on this page as well: wikibooks.org/wiki/JavaScript/Debugging

javascript depends on the browser you are using (thus compatibility problems). To debug explorer you may use this: Microsoft Script debugger

you can use jsdt, you can get some information from https://code.google.com/p/jsdt/

Using the IE8 'Developer Tools' to debug earlier IE versions

I am less than satisfied in my HTML/CSS/JS debugging of pages with IE6 and 7 specific bugs.
I am aware that IE8 has a Firebug clone, called 'Developer Tools' installed.
Is it possible to have IE8 installed (maybe on a VM, i don't mind), set it to compatibility mode (is there one for IE6?), then perform JS debugging and live HTML changes, using the IE8 Developer Tools, just like we can in Firebug?
many many thanks
mieze

There are differences between native IE6/7 and the IE8 compatibility mode:
http://blogs.msdn.com/ie/archive/2009/03/12/site-compatibility-and-ie8.aspx
The best option I've found to debug in IE6/7 is to install the Microsoft Script Editor (not Debugger), that is bundled with Microsoft Office. It's an optional install, so you probably have to open Add remove programs in Control panel and go through setup again. Here's a guide to configure IE after you've installed the Microsoft Script Editor.
http://www.jonathanboutelle.com/mt/archives/2006/01/howto_debug_jav.html
The default view doesn't have breakpoints and such, so take a look at the menu to add the views you like. It's not as good as Firebug, but it's a lot better than alert-debugging ;)

I've said it before, and I'll say it again:
Firebug Lite
That'll let you use Firebug features in whatever browser you feel like using that day...

The most satisfying IE6/7/8 javascript debugging experience I've had is with Visual Studio. And you don't have to shell out the beaucoup bucks to get it either since the Express edition has the same debugger as the higher SKUs.
Install Visual Studio Express Edition (Download)
Create a new project
Click debug to start the empty project
You now have an instance of IE running in a world class debugger!
Just point the browser at your test URL and set breakpoints to your hearts content!

You might want to try MS javascript debugger http://www.microsoft.com/downloads/details.aspx?FamilyID=2f465be0-94fd-4569-b3c4-dffdf19ccd99&displaylang=en
Not without its share of problems though

The IE8 dev tools is an upgrade of the IE Developer Toolbar, which is available for 6 & 7. It doesn't do debugging, but will let you inspect the DOM, etc. Combining it with the JS debugger (as in other answers) is as good as you can get, afaik