Facebook is said to be looking at a couple of companies to add to its ever-growing list of acquisitions. Rumor has it that the company is looking at the Opera browser to pad out its mobile presence. The company’s Opera Mini mobile browser has a reported 170 million users, according to Reuters, and could give the social network an in with mobile phone manufacturers and operators.

Shares of Opera’s Norway-based parent company soared over 20 percent on the news, the Reuters report said, with analysts speculating that the deal could be another $1 billion acquisition for Facebook, following its high-priced deal for Instagram.

Mobile, of course, has been the main concern about Facebook’s future, and the company has said it has yet to work out how best to deal with the rapid shift to mobile browsing. By acquiring a full-fledged mobile browser, Facebook would have the infrastructure in place for whatever its mobile plans may be. Opera works on many platforms and syncs between tablets, phones and desktops — something that ought to appeal to the social network.

Another rumor that’s been popping up is that Facebook is looking into acquiring Face.com, a facial recognition service from Israel. The Next Web reports that Israeli publications say that Facebook is interested in the service, which could scan and identify faces in an uploaded photo. According to the report, Face.com has been a previous acquisition target for the social network, but the two companies have never managed to strike a deal. Facebook may gain some control of the company in a non-traditional way. GigaOm reports that Facebook could be buying stake in the company from the Moscow-based search engine Yandex, in exchange for cash and Facebook stock.

Facebook is obviously interested in providing a comprehensive photo-sharing experience. It not only bought Instagram, but also released its own iOS app for photo-sharing last week. Facebook Camera offers Instagram-like filters for folks who want to add a little extra something to their mobile snaps. The app also presents just the photos from your news feed — similar to apps such as Pixable — and makes it easy to upload mobile photos to the Web site.

Finally, the company is said to be working on a Facebook phone and reportedly hired several former Apple engineers to work on the project. According to a report from the New York Times, the company is working on making its own smartphone by next year. Unnamed sources told the Times’ Nick Bilton that Facebook has hired at least six former Apple software and hardware engineers who worked on the iPhone and at least one who worked on the iPad.

A Facebook phone would be an interesting move for the company, which has never made any hardware and has been focused on building out its software to create a broad platform for desktop and mobile applications. But this is not the first time that rumors about a Facebook phone have come up, and the company has worked with HTC in the past to bake its social network into the HTC Status.

It will be hard for Facebook to crack the mobile phone market, particularly as Apple and Samsung continue to make mobile phones an increasingly two-horse race. There are a host of extra problems that come with moving into smartphones such as manufacturing and distribution. Facebook could, of course, likely acquire a smartphone maker — the Times report floats HTC as a possible candidate.

Facebook declined to comment on the acquisition or hardware rumors.

(Washington Post Co. Chairman and chief executive Donald Graham is a member of Facebook’s board of directors.)

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