Firefox tip – Extensions in beta versions
Here is a quick Firefox tip: If you are running a beta version of Firefox (e.g. 3.5b4 / 3.5 beta 4), and you are trying to install an extension or theme, it won’t let you. The extension page will disable the install button. Here is how you trick it into working. Note that this could cause Firefox to crash randomly. If that happens, start firefox in safe mode and uninstall whatever you installed.
Go into about:config and search (using the filter box) for ‘useragent’. Find the entry called ‘general.useragent.extra.firefox’, double click it, and change the value from ‘firefox/3.5b4’ (or whatever it says) to ‘firefox/3.0’.
After you restart Firefox, the extensions site should allow you to install. But when you try, you will have another problem. Firefox will determine that the extension you are trying to install is not intended for this version of Firefox.
To fix this, go back to about:config, right click and select new>Boolean. When it asks you for the name, enter ‘extensions.checkCompatibility’. When it asks you for the value, set it to false.
Now you should be able to install new extensions or themes in a beta version of Firefox.