Tabs on mozilla.org have a hover state to show which tab is currently highlighted but have no current state to show which one is selected. The exception is the 'Store' tab which changes white when you select it. Screenshots are included at http://forums.mozillazine.org/viewtopic.php?t=190924
The CSS for this is allready there, but the difficulty is that there is no easy way for the site build scripts to know what section of the site each page is part of. The store was easy, because it is actually a different set of files on a separate server, all of which (obviously) are part of the "store" tab. To turn "on" a tab, there is a body class setup for each tab (ex. <body class="sectionStore">).
No place to vote here?
This is pretty much fixed now. I'll leave it open since there are a few sections that don't work yet (Developers, and the Firefox and Thunderbird Help sections).
Also, I suspect, anything in NOMENU. I've been thinking we need a better way of doing this stuff (NOWRAP, NOMENU). Comments at the top of the file would probably work, and could also be extended to give a breadcrumb title and a breadcrumb parent page (from which the proceeding titles would come). We could even pick the appropriate section out of the breadcrumb parent chain.
Another option is to have a sitemap.xml file that defines the structure of mozilla.org. (As is done for developer.mozilla.org.)
If we're going that far we should just switch to DevMo's build system. But Steven has fixed this for most high-profile pages through the templates.
Resolving as fixed. Although this was opened to refer to an older site design, the new site design does highlight the section link for pages within that section. Note that there's a lot of content on the site that's not part of one of the top-level sections, so not all pages have highlighting in the main nav.