One thing that has troubled firefox users after upgrading to firefox 3 is that they are not able to install some of the addons that say the the "addon is incompatible with firefox 3".
But now there is a little tweak that may help firefox users out of this problem.
First you need to type "about:config" in the URL bar in Firefox 3. Note: no quotes when typing this. You'll be warned that you're mucking about with the settings. Just click the "I'll be careful, I promise!" button and you'll see tons of application preferences.
The one you want actually isn't there, so don't bother looking for it. Instead, right click to create a New, Boolean preference. Type "extensions.checkCompatibility" (again, no quotes) as your preference and then choose the value of False for it. Restart Firefox and you should be able to install any Firefox extension.
This doesn't mean that your older extension will work perfectly; after all, it was designed for Firefox 2 or earlier. However, you can at least install and try it. In fact, my gut tells me that this preference is to aid extension developers, which is why it's not included by default.
Remember that you could hose up your Firefox settings and behavior with these types of tweaks, so if you're not willing to take and accept that risk, stay away from "about:config".
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