Firefox and browser lock-in
Browser lock-in is subtle, and Firefox developers should do everything they can to decrease it.
So I download Firefox, and I want to make it my standard browser. I open it. I'm browsing around, and it takes me a while to figure out how to create new tabs instead of new windows. Developers, make ctrl+N open up a new tab, not a new window. Make clicking a link that opens a new window open up in a new tab. Tabs are a major selling point, they should be the default.
I come across a page I like and I want to blog it. But my bookmarklet is on IE, not here. Developers, make an IE bookmarks import function come up automatically the first time I run Firefox. Have it ask me if I'd like to import the bookmarks. Make it painless. I'm at work and have no time to go hunt around for how to import bookmarks.
So I decide to spend a few minutes to create a bookmarklet here. (I'm motivated - I want to use those tabs!) I go to my movabletype page, and it asks me to login. I have long since forgotten my password (IE keeps me logged in forever). So I can't login and I can't ask for my password because I'm at work and the password gets sent to my home email. Developers, make Firefox import cookies when it imports bookmarks.
The end result is that I am forced to go back to IE, and Firefox may just sit on my computer never to be used again unless I find some time to set up all these things.