No longer works with Firefox 10.0 Rated 1 out of 5 stars
Rather ironic, but Firefox 10.0 breaks the basic mechanism behind the "Add-on Compatibility Reporter". It is no longer possible to enable "incompatible" add-ons (the same ones I've been using up to 9.0.1, some of which haven't been "compatible" since 3.5).
The developer reply says that it is "by design" that Firefox 10 + ACR disables (with no obvious way to enable) known compatible add-ons. That is why I feel my rating stands. ACR is not a useful add-on.
To get around this breakage in Firefox 10, open "about:config" and in the filter type "compat". If you see "extensions.checkCompatibility.10.0", click it to set it false. Otherwise, right click and add a new boolean with that name, value false. Restart firefox.
Firefox 10 is the first compatible-by-default public Firefox release. From now on, the ACR is not flipping compatibility because it does not work well with compat-by-default. Compat-by-default does not enable some add-ons, including those not available for Firefox versions 4+. So, this is by design.