User-Agent: Mozilla/5.0 (X11; U; Linux i686; it; rv:1.9b5) Gecko/2008050509 Firefox/3.0b5 Build Identifier: Mozilla/5.0 (X11; U; Linux i686; it; rv:1.9b5) Gecko/2008050509 Firefox/3.0b5 Dom Inspector - as extension (https://addons.mozilla.org/it/firefox/addon/6622) - cannot be installed because compatibility is declared as "3.0a1 - 3.0.*", and current version (b5) doesn't match the "filter". Reproducible: Always Steps to Reproduce: 1.Browse to https://addons.mozilla.org/it/firefox/addon/6622 2.Click on "add to firefox" 3.Wait for the extension to download and see the error message Actual Results: Extension can't be installed Expected Results: Extension is downloaded and installed DOM Inspector page (http://www.mozilla.org/projects/inspector/) isn't referring yet to the extension. the "Use the conveniently named "DOM Inspector" component in Bugzilla." part isn't effective, and leads to misunderstanding (DOM Inspector component can't be found)

What error do you see when you attempt to install?

"DOM Inspector 2.0.0 cannot be installed because it's incompatible with 3.0b5." (it's not actually the exact error message, i'm translating it)

Are you using Mozilla's version of Firefox or the one provided by your linux distribution?

It happens both with the version shipped with my distribution (Ubuntu 8.04) and with the package downloaded from Mozilla website.

By switching between Mozilla and Ubuntu's Firefox you will have hit bug 433371. You must delete the extensions.rdf and extensions.cache files from your profile.