Normally you can simply install the older version right over the newer one. Your bookmarks and plugins are stored in a separate location and are unaffected by this.
Cometbird is Firefox, so when you have questions, you can simply visit the Firefox site for answers.
Thank you! I went ahead and reinstalled and it was working great, until Norton kicked in to do a scan. It was detecting the plugin-container.exe for cometbird as a security risk and quarantined it. Once I restored the file, it is back to working like a charm!
The plugin-container.exe process is vital, since Adobe Flash Player, Quicktime and Silverlight plugins will be kept there, in case CometBird crashes (plugin-container.exe avoids CometBird to crash fully if any any of these plugin does respond). If any of these plugins crash, all you’ve got to do is just reload the conflictive page and that’s it.