Emulsions, foams or polymer microgel suspensions are jammed assemblies of soft deformable elements in a liquid matrix. At the macroscopic scale, they behave as yield stress fluids, intermediate between solids and liquids. Beyond this complex bulk rheology, such fluids also exhibit slip at the walls, due to sheared liquid lubrication layers between the soft spheres and the solid surface. Measuring and predicting the corresponding friction laws which relate slip velocity and wall stress is crucial for applications, but also provides information on the dissipation mechanisms. In particular, the coupling between hydrodynamics and the elastic or capillary deformation of the microstructure leads to non-linear friction regimes. In this seminar, I will present experimental results of wall friction of foams and polymer microgels. We evidence transitions in wall slip regimes, from non-linear to linear friction. These transitions depend not only on how jammed the soft elements are, but also on the applied stress at the wall.