What's the difference between the Bab and Bah'ullah?
Do Bahais believe these men ever performed any miracles?
While Baha'is regard both the Bab and Baha'u'llah as Manifestations of God, we consider the Bab also to be the forerunner of Baha'u'llah. As for miracles, I would say both men performed miracles but we don't talk about them that much because Baha'is don't consider miracles as proof of the truth of a revelation. However, there is a rather spectacular miracle associated with the martyrdom of the Bab. An Armenian regiment had been charged with the duty of executing the Bab by firing squad. Sam Khan who headed that regiment, approached the Bab: 'I profess the Christian Faith and entertain no ill will against you. If your Cause be the Cause of truth, enable me to free myself from the obligation to shed your blood.' To this the Báb replied: 'Follow your instructions, and if your intention be sincere, the Almighty is surely able to relieve you from your perplexity.'
"The Báb and His disciple were suspended by ropes from a nail in the wall, the head of Mirza Muhammad-'Ali resting on the breast of the Báb. Seven hundred and fifty soldiers were positioned in three files. Roofs of the buildings around teemed with spectators.
Each row of soldiers fired in turn. The smoke from so many rifles clouded the scene. When it lifted the Báb was not there. Only His disciple could be seen, standing under the nail in the wall, smiling and unconcerned. Bullets had only severed the ropes with which they were suspended. Cries rang out from the onlookers: 'The Siyyid-i-Báb has gone from our sight!'
A frantic search followed. The Báb was found, sitting in the same room where He had been lodged the night before, in conversation with His amanuensis. That conversation had been interrupted earlier in the day. Now it was finished and He told the farrash-bashi to carry out his duty. But the farrash-bashi was terror-stricken and ran away, nor did he ever return to his post. Sam Khan, for his part, told his superiors that he had carried out the task given to him; he would not attempt it a second time. So Aqa Jan Khan-i-Khamsih and his Nasiri regiment replaced the Armenians, and the Báb and His disciple were suspended once again at the same spot. The Nasiri regiment fired. The bodies of the Báb and His disciple were shattered, and their flesh was united."
— H.M. Balyuzi
Unlike the miracles associated with Christ, we don't just have the testimony of Christians for this event. Here is a Western account:
The founder of the sect has been executed at Tabreez. He was killed by a volley of musketry, and his death was on the point of giving his religion a lustre which would have largely increased his proselytes. When the smoke and dust cleared away after the volley, Báb was not to be seen, and the populace proclaimed that he had ascended to the skies. The balls had broken the ropes by which he was bound, but he was dragged from the recess where after some search he was discovered and shot. His death, according to the belief of his disciples, will make no difference as Báb must always exist.
— Sir Justin Shiel
There are also accounts by Shi'ite clerics very antagonistic towards the religion but even they admit the following, although they differ as to what happened to Anis.
1. The Báb and Anís were suspended about three meters above the ground on a rope and fired on by a Christian regiment.
2. The bullets cut the rope and one bullet wounded Anís.
3. The Báb ran into one of the rooms in the barracks.
4. The Báb was brought back out and he and Anís were shot again, this time fatally.