This clinical trial studies capecitabine and celecoxib in treating patients with solid malignancies that are metastatic or cannot be removed by surgery. Drugs used in chemotherapy, such as capecitabine, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Celecoxib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving capecitabine and celecoxib together may be an effective treatment for solid malignancies.