Is browsing the internet and using programs not beneficial for work on the company's device and during working hours considered unlawful (haram)?

The fundamental principle is that work should be performed according to the conditions agreed upon between the worker and the employer, as long as these conditions do not contradict Islamic law. This is based on the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions, except for a condition that forbids what is lawful or permits what is unlawful." If the employer permits the use of work tools or the utilization of work time for purposes other than the work's interest, then there is no objection to that. Otherwise, it is not permissible.