Firefox 16, and newer Firefoxes as well, are affected by a bug that sometimes interferes with add-on actions. It's a very specific bug and it's not considered problematic or widespread enough to warrant an update, so it won't be fixed until Firefox 17 comes out, six weeks from now.
"The problem is that the window load event handler that many add-ons depend on isn’t fired under some circumstances," Mozilla's add-on developer relations lead Jorge Villalobos wrote.
"So far it appears that this only happens when a popup window is opened, and only in cases where the domain in the new window is different from the one that opened the window," he explained the issue.
"Since most add-on scripts rely on the load handler being called, many of them will not work in the newly opened popup window," he added.
As you can see, it's fairly hard to run into the problem and shouldn't affect too many add-ons. Even for the ones affected, the damage should be minimal, which is why Mozilla decided to skip on updating Firefox 16 to fix this.
However, if you do find you are experiencing big problems because of the bug, you can get in touch with Mozilla and explain your situation. The bug is listed here.
Mozilla may consider issuing an update if it finds the problem is worse than it estimated. At the same time, some other bug may show up that is worse than this one and that one will warrant an update, Firefox 16.0.1. If that is the case, you can be sure a fix for this bug will be bundled as well.
Firefox 16 is now in the stable channel and is making its way to hundreds of millions of users around the world.
The latest update comes with some performance improvements, the new incremental garbage collector should ensure smoother runs, better support for some cutting-edge web technologies and new tools for developers.