Zynga introduced a web browser toolbar for its Mafia Wars role-playing Facebook game last November with the intention of increasing engagement among serious players. Apparently the results were good, because it launched a toolbar for smash-hit farming game FarmVille just this week.

And now, more than three years after Facebook launched a browser toolbar for Firefox in English, it has introduced an upgrade. Internet Explorers users (most people on the web) can now install it, too, and both versions now support 16 languages, including Arabic, Chinese (simple and traditional), Danish, Dutch, German, Spanish (Spain and international), French, Hebrew, Indonesian, Italian, Japanese, Portuguese (Brazilian), Swedish and Turkish.

Why all these toolbars now? To get more people coming back more often. The Facebook one lets you see new pokes, friend requests, invitations and messages. You can set it to show a pop-up when friends update profiles and status, upload photos and take other actions. It also doubles as a bookmarklet — click the “Share” button and you can post the page you’re on to your news feed and profile, or message it to your friends. Other features include side window you can open to view the latest status updates from your friends, a search box that lets you search Facebook and a drop-down menu of links to part of the Facebook home site. The Firefox version also lets you update your own status from the bar, and click to view your latest event invitations.

For any serious Facebook user on IE, the toolbar is worth checking out. The Firefox bar, from what AppData shows us, has a small but loyal group of followers — the numbers aren’t too surprising given the lack of promotions Facebook has given it over the years.

And, for those FarmVille players who are keen to stay connected to their crops, the game’s new toolbar is a little simpler than Facebook’s — it gives you an easy way to track your bonuses and watch the time you have left before a virtual harvest. If you click on the drop-down menu that says “FarmVille,” you can see the option to choose other Zynga game toolbars — only Mafia Wars, so far.

In sum, the toolbar feature is hardly new, but clearly both Zynga and Facebook think that it’s a good way to increase engagement. However, for the millions of people who are both serious Facebook users and big Zynga gamers, they may end up with a couple toolbars installed — convenient, but not the most elegant user interface.