You have a crummy router and a crummy bit, but it is an easy cut on soft
wood. You ought to be able to do it in one pass. A more difficult cut on
oak wouldn't stand a chance in one pass.
If you are doing the ends, you might want to do a few passes on them though.
I have never routed fir, but end grain can be tricky.
Since you have not routed before, there is one very odd thing you should
know. You have to move fairly fast without hesitation. If you go too slow
or stop, you will leave a burn that can be hard to get out.
It goes without saying that a router can do a lot of damage very quickly, so
be careful. It is certainly safer than a table saw, but it still requires