1) The new theme is too bulky, inconsistent on different platforms, and inferior to the highly refined and very user friendly theme of 1.5 (this is despite late efforts by Mozilla to spruce up the icon set and improve consistency)

2) Antiphishing technology is both weak (blacklist based) and a potential privacy problem. The privacy issues are raised because Firefox 2.0 Antiphishing Features employ an engine previously released by Google, which has been shown to potentially cause privacy risks.

3) The new Options dialog box is confusing, poorly designed, and illogically hides important features

4) There are many reported compatibility issues with the large existing libraries of extensions, themes, and plugins currently avaialble for earlier versions of Firefox. While this can, to some degree, be expected, the loss of this huge user contributed extension base is a non-trivial problem with Firefox 2.0, and could be a deal breaker for some people all by itself

5) The well known memory leak issue, which causes the Firefox browser to consume ever increasing amounts of RAM, eventually leading to sluggish performance and crashes, has been carried over into yet another generation. This is despite an enormous amount of public commentary and user requests for resolution prior to release of a new version of Firefox

6) There are reported problems with the CSS engine in Firefox 2.0, affecting various websites, and making certain features unavailable to surfers. Notable among these is a continued problem with certain aspects of Yahoo! mail

7) Reports indicate that episodes of random freezing during use are worse with the 2.0 version, though a cause has not yet been isolated

8.) Numerous users have reported that the History bar is buggy, and that in some instances - for unknown reasons - will not display recent items when the history menu is opened as a side panel

9) RSS feed handling has taken a step backwards, and is inferior to that of IE7.