I agree it doesn't always work right - lots of times it depends on what site you are on. So far I have found it doesn't work on sites like this one, or the getting started site, etc. There are lots of features in the extension that simply do not work in firefox right now last I checked, like webgl rendering, so there are a lot of ways to break the extension and many places it doesn't work. Thats why its experimental mode still.

Thanks for the feedback.... one comment though is that instability might be normal thing to expect in the dev channel or nightly build, and instability of this extension in those channels might be unavoidable at times no matter what steps are taken to improve the extension. In spite of that there could be a race condition or something where depending on the speed of the computer and the exact site being visited no feature of the extension will work or it may work inconsistently. I hope this is not the case but it could be one possible thing that could explain some of the instances the extension not working as expected.

There are very similar issues that plague the chrome version from time to time. Sometimes the content scripts just don't run, or fail to be evaluated when we detect they didn't run, etc.

I will at some point try to at least show the right message for "cannot run on this page" when I am sure what set of pages this rule will apply to.... and may try some fallback image when webgl doesn't work.