Chromium browsers do not allow you this choice. There, the philosophy seems to be that the web is a designer-driven layout medium and that the viewer should not have accessibility choices.
Btw, some of the "sites worse", if you're referring to Google, that's them just breaking things intentionally. You can sometimes work around it by specifying a different useragent and then things are fast again until they change things again.
As a browser, Firefox is standards compliant. I agree there are many applications that use a web interface as the GUI and a bunch were coded for IE6 or IE6 with ActiveX and don't display well (or at all) in Chrome. It really depends, but the problem isn't that Firefox follows standards, but that the developers did not follow standards.