An offshore subsea wellbore activities system comprising: - an offshore vessel having a hull subjected to heave motion, said vessel being provided with: - a tower, - a well center through which a firing line extends, - a heave compensated hoisting device, providing a heave compensation mode, - a vertical motion arm rail (60,61) along said tower, - a motion arm assembly (70,71,72,80,81,82) comprising a base and an extensible and retractable motion arm, wherein the base is guided by said at least one vertical motion arm rail (60,61), - a motion arm assembly vertical drive which is adapted to move the motion arm base along said vertical motion arm rail (60,61) relative to the tower, - a wellbore activities device comprising a riser tension frame, wherein said riser tension frame comprises: - an upper frame section adapted to be suspended or suspended from said heave compensated hoisting device, - a lower frame section provided with a riser attachment device adapted to attach a riser to said lower frame section so as to extend in the firing line, - vertical riser load bearing structure, e.g. formed by struts (230, 231, 232), connecting said lower frame section to said upper frame section, wherein said wellbore activities device further comprises: - a coiled tubing injector, - a wireline lubricator, - one or more pressure control devices (320, 420) associated with said coiled tubing injector and/or said wireline lubricator, wherein each of said coiled tubing injector and said wireline lubricator is received by and individually movable within said riser tension frame between a parking position remote from said firing line and an operative position aligned with said firing line allowing to use a selected one of said coiled tubing injector and said wireline lubricator for performing a coiled tubing operation or a wireline operation respectively when aligned with the firing line, and wherein the wellbore activities device provides a lateral firing line access passage having a height of at least 40ft. (12.2m) and a width of at least 1 ft. (0.35m) J Z allowing to transfer an elongated wellbore tool or a wellbore tubular in vertical orientation thereof by means of the motion arm assembly (70,71,72,80,81,82) in a substantially lateral motion between a remote position outside of the riser tension frame and an operative position within the riser tension frame and aligned with the firing line. - an offshore vessel having a hull subjected to heave motion, said vessel being provided with: - a tower, - a well center through which a firing line extends, - a heave compensated hoisting device, providing a heave compensation mode, - a vertical motion arm rail (60,61) along said tower, - a motion arm assembly (70,71,72,80,81,82) comprising a base and an extensible and retractable motion arm, wherein the base is guided by said at least one vertical motion arm rail (60,61), - a motion arm assembly vertical drive which is adapted to move the motion arm base along said vertical motion arm rail (60,61) relative to the tower, - a tower, - a well center through which a firing line extends, - a heave compensated hoisting device, providing a heave compensation mode, - a vertical motion arm rail (60,61) along said tower, - a motion arm assembly (70,71,72,80,81,82) comprising a base and an extensible and retractable motion arm, wherein the base is guided by said at least one vertical motion arm rail (60,61), - a motion arm assembly vertical drive which is adapted to move the motion arm base along said vertical motion arm rail (60,61) relative to the tower, - a wellbore activities device comprising a riser tension frame, wherein said riser tension frame comprises: - an upper frame section adapted to be suspended or suspended from said heave compensated hoisting device, - a lower frame section provided with a riser attachment device adapted to attach a riser to said lower frame section so as to extend in the firing line, - vertical riser load bearing structure, e.g. formed by struts (230, 231, 232), connecting said lower frame section to said upper frame section, wherein said wellbore activities device further comprises: - a coiled tubing injector, - a wireline lubricator, - one or more pressure control devices (320, 420) associated with said coiled tubing injector and/or said wireline lubricator, - an upper frame section adapted to be suspended or suspended from said heave compensated hoisting device, - a lower frame section provided with a riser attachment device adapted to attach a riser to said lower frame section so as to extend in the firing line, - vertical riser load bearing structure, e.g. formed by struts (230, 231, 232), connecting said lower frame section to said upper frame section, - a coiled tubing injector, - a wireline lubricator, - one or more pressure control devices (320, 420) associated with said coiled tubing injector and/or said wireline lubricator,