I am against including the tag in the title. I wrote the following first at meta.emacs.stackexchange.com by mistake, then found this question here.
I would prefer that the window-manager title bar (or the tab label, if using tabs) reflect only the question title, and not have the first tag prepended to the title.
Especially when there are multiple tags for a question, the order is not necessarily signifiant. So why pick the first one to prepend?
But really, why prepend any tag?
I'm using Google Chrome, and at least with this browser, this is the behavior I see.
Here is one example. The tab title shows this: text properties - com. In this case, because the first tag (text properties) is fairly long, after the first 3 chars of the question title, com, the rest of it is truncated.
So we learn a lot from the page (or tab) title about the first tag, but we learn next to nothing about what the question is.
IMHO, the best label for the question's tab (or page) is the question title itself - no "helpful" adornments. Just one opinion.
In response to the reasons given for this page/tab title munging, I would say that these components of a web page are for users. They are for quickly locating a given page or tab among many that might be open.
They are not first and foremost for web developers or search engines. My advice here is Hands off! - this is a user browsing convenience. It's not for you to fiddle with in attempts to struggle with web indexers and such. Please find another terrain for that combat, and leave the visible components of a user's browser for use by the user.