Forbes.com called Firefox the best browser in a 2004 commentary piece. PC World named Firefox the "product of the year" in 2005 on their "100 Best Products of 2005" list. After the release of Firefox 2 and Internet Explorer 7 in 2006, PC World reviewed both and announced that Firefox was the better browser.
Internet Week ran an article in which many readers reported high memory usage in Firefox 1.5. Mozilla developers said the higher memory use of Firefox 1.5 is at least partially an effect of the new fast backwards-and-forwards (FastBack) feature. Other known causes of memory problems are misbehaving extensions, such as Google Toolbar and some old versions of Adblock, or plug-ins, such as older versions of Adobe Acrobat Reader. When PC Magazine compared memory usage of Firefox, Opera, and Internet Explorer, they found that Firefox seemed to use only about as much memory as the other browsers. Tests performed by PC World and Zimbra indicate that Firefox 2 uses less memory than Internet Explorer 7.
Softpedia notes that Firefox takes longer to start up than other browsers, which was confirmed by browser speed tests. IE also launches slightly faster than Firefox on Microsoft Windows since many of its components are built into Windows and are loaded during system startup.