The Mozilla Foundation may have just released its latest update to the popular Firefox browser, but some users say their patience with the software's flaws is beginning to wear thin.

Firefox rose to popularity after its 1.0 release in November 2004 as an alternative to Microsoft Internet Explorer, lacking that browser's most serious security flaws. Now that the novelty has faded, however, some users are highlighting Firefox's shortcomings compared with competitors such as IE, Opera, Apple's Safari and the KDE project's Linux-based Konqueror.

One issue that has been getting attention since the Wednesday release of Firefox 1.5 is a bug that causes Mac OS X systems to use 100 percent of available processor resources in some cases, such as when scrolling in some Web-based applications (such as Google Maps) and holding down the mouse button.

The bug has been known since before the release of Firefox 1.0, but has never been fixed, critics noted. (The Mozilla project has assigned the issue bug no. 141710.)

Some users said the bug makes it difficult to use Firefox on laptops, because it causes the fan to run more frequently and uses up battery power. "I am going to have to recommend that any Mac users I know stay away from Firefox until this is fixed. It makes Google Maps virtually unusable, and it chews up battery, and causes lots of heat in laptops," wrote one user on the Bugzilla bug-tracking site.

"It is seriously getting time to get this fixed," wrote another.

Others said the bug was not particularly serious, was not noticeable to users on desktop systems and would, in any case, disappear when the browser shifts to a newer programming interface called Cocoa.

Another specific gripe is the lack of Acid2 compliance. Acid2 is a test from the Web Standards Project (WaSP) designed to test a browser's support for W3C standards such as CSS1, HTML4 and PNG. Most browsers - including IE and Opera - admit they won't pass Acid2 for some time; for example Microsoft has said IE 7 won't pass.

The issue has become more urgent recently, however, because Konqueror's latest release - appearing this week with KDE 3.5 - passes Acid2. Apple's Safari, which shares some code with Konqueror, also recently became Acid2 compliant. Firefox is not expected to pass the test until version 2.0.

Others said Firefox 1.5 introduced new glitches. Issues mentioned by users after their first few hours with Firefox 1.5 included the "reload" button disappearing, a bug with selected text, problems with cookie management, keyboard shortcuts being randomly disabled, and a Mac-specific problem with the URL window.

Firefox has had increasingly serious issues with security as its user base has exploded. Among this year's flaws was a highly dangerous one ironically leaving Windows and IE untouched while affecting Firefox and Linux. Another flaw involving IDN parsing required a patch to be rushed out. A report from Symantec revealed that nearly twice as many flaws had been discovered in Firefox as in Explorer over the first six months of this year.