A system for solid freeform fabrication of an object, comprising: a solid freeform fabrication apparatus having a plurality of modeling material dispensing heads and a plurality of support material dispensing heads each dispensing head comprising an array of nozzles; a building material supply apparatus comprising a building material flow unit configured to supply a plurality of building materials to said fabrication apparatus, said plurality of building materials comprising at least one support material and at least one modeling material, wherein said flow unit is arranged to allow flow of different building materials to different dispensing heads, such that said at least one modeling material flows into at least one modeling material dispensing head and said at least one support material flows into at least one support material dispensing head; and a control unit configured for controlling said fabrication apparatus and said building material supply apparatus, based on an operation mode selected from a plurality of predetermined operation modes, wherein said plurality of operation modes comprises at least a first operation mode in which all dispensing heads operate during a single building scan cycle of said fabrication apparatus, and a second operation mode in which at any point during a buildup of a layer by said fabrication apparatus, at least one of said dispensing heads is not activated to dispense building material; and wherein said control unit is designed and configured to reduce a dispensing rate of said at least one support material dispensing head when said operation mode is said second operation mode to maintain equal layer heights for said modeling and support materials, by (i) temporarily disabling some of the nozzles in said at least one support material dispensing head, (ii) reducing a bias voltage on said at least one support material dispensing head, or (iii) disabling one or more of said support material dispensing heads. a solid freeform fabrication apparatus having a plurality of modeling material dispensing heads and a plurality of support material dispensing heads each dispensing head comprising an array of nozzles; a building material supply apparatus comprising a building material flow unit configured to supply a plurality of building materials to said fabrication apparatus, said plurality of building materials comprising at least one support material and at least one modeling material, wherein said flow unit is arranged to allow flow of different building materials to different dispensing heads, such that said at least one modeling material flows into at least one modeling material dispensing head and said at least one support material flows into at least one support material dispensing head; and a control unit configured for controlling said fabrication apparatus and said building material supply apparatus, based on an operation mode selected from a plurality of predetermined operation modes, wherein said plurality of operation modes comprises at least a first operation mode in which all dispensing heads operate during a single building scan cycle of said fabrication apparatus, and a second operation mode in which at any point during a buildup of a layer by said fabrication apparatus, at least one of said dispensing heads is not activated to dispense building material; and wherein said control unit is designed and configured to reduce a dispensing rate of said at least one support material dispensing head when said operation mode is said second operation mode to maintain equal layer heights for said modeling and support materials, by (i) temporarily disabling some of the nozzles in said at least one support material dispensing head, (ii) reducing a bias voltage on said at least one support material dispensing head, or (iii) disabling one or more of said support material dispensing heads.