The participants of this study will have relapsed/refractory follicular lymphoma. Follicular lymphoma is a type of blood cancer. It is referred to as ‘relapsed’ when the disease has come back after treatment and ‘refractory’ when treatment no longer works. Stage 1 of this trial will study the safety and the level that adverse effects of each of the study drug combinations can be tolerated (known as tolerability). It is also designed to establish a recommended study drug dosage for stage 2 and 3. Stage 2 and 3 will evaluate and compare how long participants live without their disease getting worse when receiving the study drug in combination with other drug treatment versus placebo (dummy drug) and other drug treatment.