Update: Britney Spears Spends Her 28th Birthday Shopping at Fred Segal

Happy Birthday, Britney Spears!

Just back from her "Circus" tour's stint in Australia, the pop star celebrated her 28th birthday in L.A. indulging in one of her favorite pastimes: shopping!

See shots of Britney's bikini body in this slideshow

Going casual in oversize black glasses, a tan and black hat, white long-sleeve tee and a black sweater, the singer hit L.A. boutique Fred Segal with beau Jason Trawick.

After browsing the mens' sportswear section, she picked up some gifts not for herself but for her sons Sean, 4, and Jayden, 3.

It's been a great year for Spears after a seriously rocky period: her world tour went off without a hitch, she scored yet another #1 single in October with "Three," her body's back in prime condition...and, following a string of Mr. Wrongs, she has found a new, stable love in Trawick, 37.

Britney rocks it! See photos from her blockbuster world tour

A pal tells Us that Trawick is "absolutely fantastic with the boys." And the agent stood by Spears in her darkest days: in early 2008, she was involuntarily committed twice to a psychiatric hospital; in 2007, she had lost custody of her sons.

What should Britney be most thankful for this holiday season?

One of Trawick's biggest fans? Britney's mom Lynne Spears. "Lynne said, 'He's the kind of man you would dream of your daughter marrying. The kids love him, and he's stable,'" a friend tells Us.