Where can I find a document which succinctly describes all the backward-compatibility which has been lost or eliminated with Firefox 3.6.xx in the areas of features, plug-ins, etc.?
I have been unable to find any specific info on backward compatibility issues. Asking people to move to a new version without such info being available is unrealistic.
Additional System Details
- Gecko default plugin
- Runs Java applets using the latest installed versions of Java. For more information: Java Embedding Plugin. Run version test: Java Information.
- The Flip4Mac WMV Plugin allows you to view Windows Media content using QuickTime.
- Version 188.8.131.5298
- Google Talk Plugin Video Accelerator version:0.1.43.3
- Java Plug-In 2 for NPAPI Browsers
- The QuickTime Plugin allows you to view a wide variety of multimedia content in web pages. For more information, visit the QuickTime Web site.
- Shockwave Flash 10.2 r152
- User Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:184.108.40.206) Gecko/20110420 Firefox/3.6.17
You can see whether your extensions are compatible with Firefox 4 by installing the Extension Manager Extended add-on in Firefox 3.6. For each extension, the range of compatible versions will be listed. If your extensions list version 4.0.* or higher, they should work after the upgrade.
Regarding web pages, the resources at Firefox 4 for developers provide some information. Forums like this one will surface problems with widely used sites, but given the number of web sites in the world, I don't think anyone could compile a comprehensive list of which sites are breaking (or how badly).
Regarding features, there are some interface changes and some add-ons to restore things that were removed (such as displaying the secure site padlock in addition to a colored site info button). But really, only features important to you matter in making your decision, and you may not even realize what they are until they're gone. That's why trying it often is the best way to assess whether you want to use it.
(It's always a good idea to make a backup if you're thinking you might roll back. To back up Firefox, see Backing up your information.)