Forward only parsing is not only faster, it's less complicated which should translate to fewer bugs. It's worth noting that the HTML parser isn't used only when initially rendering the page, it's also used when rewriting the contents with JavaScript.
The bug report has a perfectly reasonable workaround you can use, and you can always put your JavaScript in a separate file or escape < >. It's a good idea to do this even with the current generation of browsers, because if you don't, you sometimes get strange bugs... often bugs that are not reproducible in all browsers.
Honestly, allowing unescaped </script> inside inline javascript wasn't a good idea to begin with.
The bug report has a perfectly reasonable workaround you can use, and you can always put your JavaScript in a separate file or escape < >. It's a good idea to do this even with the current generation of browsers, because if you don't, you sometimes get strange bugs... often bugs that are not reproducible in all browsers.
Honestly, allowing unescaped </script> inside inline javascript wasn't a good idea to begin with.