Stuck with a nasty memory leak somewhere in a large AJAX-driven application that only shows up in Firefox, and no native tools with which to diagnose it, I decided to give DynaTrace AJAX Edition a go.
DynaTrace recently added support for Firefox 11 but, unfortunately, Mozilla's ridiculous high-speed release process means the major version number was bumped just over a month later to 12. The automatic upgrades that force themselves on me when I launch Firefox(1) mean I was on Firefox 12 almost immediately, and all this put together means that I couldn't use DynaTrace.
Fortunately, we can downgrade Firefox by locating the desired release from Mozilla's FTP site(2) and installing it. As long as you don't go too far back in the release list, profiles should be reasonably safe from the downgrade; in this case, going from Firefox 12 to Firefox 11 was painless… and I got to enjoy the awesomeness of DynaTrace AJAX Edition.
Firefox will immediately begin downloading the latest version the next time you launch it, and will upgrade the time after that. So, at this point, it's worth going into Tools->Options and disabling automatic upgrades like I should have done originally.
It's time that Mozilla stopped this nonsense; incrementing the major version number so often is causing a tangible nightmare with add-on compatibility, and I cannot understand why the Firefox development team leads do not appear to care.
Note 1: Hey, Mozilla! When I launch my browser, it's because I want to visit a website, not because I want to upgrade the browser.
Note 2: "uk" stands for Ukraine, not the UK. You're looking for "en-gb", which I should already know. I mean, who was I kidding?