My site loads on most recent versions of IE fine, but on others and chrome/firefox not so well. Is there some cheatsheet that list issues of portability I can use to fix those quickly? I am only using jQuery and some ASP.
Edit: OP's comment:
I am using jquery to build a table on the fly, which contains results returned from an ajax request. I can see the results were generated, but the users claim they can't see them.
There's not really such a cheatsheet available. In general, just using a (X)HTML strict doctype and a webpage which validates and a (separate) CSS sheet which validates, should work on any webbrowser the world wide web is aware of. Once done that, the remnant of the misbehaviours/bugs are often at CSS level and MSIE-only. For that you need to learn about the common MSIE CSS bugs and fix it accordingly.
At JavaScript level you don't need to worry that much as jQuery itself is already designed to be crossbrowser compatible. As ASP is a server side view technology which just generates/sends plain HTML to the response, it has not much to do here. It's all about the HTML/CSS which you have in your own control.
Edit: made community wiki as this doesn't answer the OP's actual question and I don't want to delete the answer because others may find it useful.
There is no easy way to ensure cross-browser compatibility, but sites such as http://browsershots.org/ will help determine which browsers are displaying data incorrectly
If you are using jquery then invalid javascript could be a possible reason for the issue.
Your comments seem to indicate that your users are seeing problems that you're not able to replicate, possibly because you don't have the specific browser versions they're using. You need to see what your users are seeing. Try one of the sites that display your site as viewed by different browsers. http://browsershots.org/ is one.
I am using jquery to build a table on the fly, which contains results returned from an ajax request. I can see the results were generated, but the users claim they can't see them.
Maybe the request URL was wrong. Try with an absolute URL or a domain-relative URL (i.e. starting with /. Nevertheless, it's still shooting in the dark without an SSCCE. At least I suspect that it's just a coding mistake and that MSIE was (again) been too forgiving in that.
Update: I checked your JS code at pastebin and it turns out that you aren't using jQuery at all, but just "plain vanilla" JavaScript, with under each the MSIE-proprietary innerHTML. If you actually make use of jQuery in your webapp, then I would port all the JS to jQuery so that it will be crossbrowser compatible.