As a principle, it should be remembered that, the permissibility or impermissibility of employment in a particular firm or company basically depends on two things:
1) The nature of the job must be lawful (halal), meaning if the work entails something that is prohibited in Shariah, such as posing for nude picture-taking, serving alcohol or recording and calculating interest transactions, etc, then this type of work will be unlawful.
The reason for its prohibition is that, the work itself has been prohibited in Shariah, and due to this, even if the salary was paid from a Halal source, the work will still remain unlawful.
2) The salary or income that one receives must also be from a Halal source. If the work in itself is lawful (halal), but the salary is paid from unlawful and impure money, such as stolen or interest money, it will still be unlawful to accept that job.
Based on the above, if your job does not entail anything unlawful (even though the firm may be involved in unlawful transactions), and secondly and more importantly, the salary you receive is not from unlawful wealth, then your job will be Halal. If the salary is paid from a mixture of Halal and Haram wealth, consideration will be given to what is the majority.