With responsive designs, content should always come first

We want to retain as many features of our design across multiple platforms and viewports (rather than hiding certain parts with display: none or similar) but it's also important to consider the order in which things appear. At present, due to the order of the sidebar and main content sections of our markup, the sidebar will always want to display before the main content. It's obvious that a user with a more limited viewport should get the main content before the sidebar, otherwise they'll be seeing tangentially related content before the main content itself.

We could (and perhaps should) move our content above our navigation area, too. So that those with the smallest viewports get the content before anything else. This would certainly be the logical continuation of adhering to a "content first" maxim. However, in most instances, we'd like some navigation atop each page, so I'm happier simply swapping the order of the sidebar and content...