I think the main problem is designing for all these browsers.
Theres so many ways to code things that you may see one
code as valid but its all about how the browsers interpret
the code. You spend all this time coding then when you
check on other browsers your going crazy because it adds
3 hours of you thinking of different variables of code to add
something so simple as:

body { margin:0; border:0; }

just to get it to work in Opera.

I have seen bugs in Opera when coding but always find a variable
of recoding it to get it to work in all these browsers to design for.

Opera Mozilla FireFox Internet explorer Netscape Safari Camino

There have been issues where IE and Firefox are fine and Opera isn't.
Then there are times when Opera and Firefox are fine and IE isn't.
And the next combination as well.

For the issue above I use this:

#container { position:fixed; margin:0; top:0px; left:0px; }

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