Is it is easy to reverse engineer 5000 lines of obfuscated code? I mean sure it can be done, but it is not easy as in no effort required. It will take several days/weeks to fully understand and clean up the code. Sure you can use a beautyfier to get the initial structure, but after that that it is a tedious job to figure out the code.
As I wrote above the idea of obfuscation is not to achieve 100% protection. That is not possible for any client side code. The idea is to make it harder, so it requires at least some effort as opposed to no effort at all.
We put fences around our houses and locks on our doors. Even though we know that anyone who put in some effort can jump the fence and force the door open. It is a terrible level of protection and yet it is sufficient.
Mozilla are now asking developers to remove the door from there home, so that anyone can walk right in.
Obfuscation is not perfect, but it the best we got and it is better than most people think. Now Mozilla has decided that no protection at all is just as good as some protetion. It makes no sence and it will keep me and many others from spending time on add on development for Firefox.