If a user submits their preferences while viewing one tab after having made bad input in another tab, they stay on the same tab, but get an error message. This has the effect of making it seem that they've done something wrong on the current tab, but it's invisible, or that the page has failed to highlight the error. After a while they might work out that they need to look for the actual problem on a different preferences tab; or they might not.

The error message needs to come with a way to direct the user to the tab which needs attention. One way this could be done would be to add a visual indicator to the title of the problem tab and make everything else inert. Just moving them to the problem tab on form submission would be a jarring context change, so we shouldn't do that.

To reproduce:

• Go to the user profile tab in Special:Preferences
• Enter an invalid value into the signature field (e.g. no link to user page)
• Go to any other tab
• Click Save