Hi. Lovely game you have here. I was fascinated by brainf**k, Turing machines and was positively thrilled to find a puzzle game based on similar concepts.

Today Firefox 4 was launched and it brought with it this bug (MacOSX):
Short version: Bridging does not work. Shift functions as the 'a' key, not bridging.
Procedure to repeat:
0. Start the game in firefox 4 MacOSX (10.6.6 3GB Ram Core2Duo 2.66 GHz).
1. Launch any level.
2. Press '1', 'e' and click in the middle square.
3. press 'd'
4. press and hold 'shift' and click on the same middle square.
This should build a bridge from left to right, instead it builds a conveyor belt from right to left and overwrites the previous conveyor belt.

Workaround: Play the game in Safari instead.

I can't confirm that this problem occurs on every mac with Firefox 4, but if anyone can repeat it, please post so I know it is not just a local problem.
It worked on the same machine with Firefox 3.6 before the upgrade.