Speed Mozilla takes considerably longer to launch than any other browser. Opening a new window is slow, regularly taking between three and ten seconds (anything over one second is highly frustrating), and there are similar problems with closing and redrawing windows.
Memory Consumption To a large extent the slowness is due to Mozilla’s memory consumption, which regularly sends it into the mire of virtual memory on machines which don’t have large amounts of RAM.
Menu structure Mozilla is currently heavily lopsided towards expert users, and people who prefer using the keyboard to using the mouse: as mentioned above, it has not enough toolbar buttons, and conversely it has too many menus. Menus are the most difficult GUI control to use, so you need to keep them as simple and uncluttered as possible. Mozilla, unfortunately, does the opposite.
Migration Mozilla is woefully incomplete in these regards: You can show your Internet Explorer favorites as a folder in your Mozilla bookmarks, but you can’t import or edit them. You can’t import messages from a Netscape Communicator 4.x profile after creating a Mozilla profile, nor can you import your address book without exporting it from 4.x first. And the ability to import information from Mozilla’s main competitor, Outlook Express, is completely absent.
Shortcut Menus Shortcut menus (known as “contextual menus” on Mac OS) are a method of quick access to extremely frequent commands (such as “Back” or “Forward”). Mozilla’s shortcut menus were too long and to inconsistent for anyone to be able to use them quickly. Mozilla breaks with previous versions (and with every other kind of menu) in requiring two clicks, rather than a single drag, to select an item — doubling the amount of time taken to use the menu. The net result is that the menus are much slower to use than they could be.
Validation If a site works in Internet Explorer, and even (in many cases) in Netscape 4.x, but not in their Mozilla-based browser, without any other information users will naturally assume that the problem is with Mozilla.Solution: There are already plans to show an icon in Navigator’s status bar to notify the user if a page contains script errors, or objects which Mozilla doesn’t have a plug-in for. This would make users less angry with Mozilla when a page does not render properly.