Many developers recommend Firefox for web development for a variety of reasons. But, after looking at Opera, it seems to me that Opera has all of the same web development functionality that Firefox has built into it. So what is wrong with Opera for web development?
I think any browser you like to work in is the right browser to work in. I like Chrome--I think its developer interface is very nice indeed.
Problem is, a very compliant browser is going to fool you when you switch to a less-compliant one (lookin at you, Internet Explorer). Things will be building nicely, and then your boss will look at it on IE6 and it'll be a calamity. So you've got to at least be looking very frequently at your work the browser that's simultaneously most popular and most breakage-prone.
That's a good point about Opera, and it has been highly-rated whenever I have heard about it.
I'm an "opera lover" and it's my browser of choice. I think the main problem with using it for web development is the rather perverse fact that it has probably the best standards compliance and hence when you view a site created primarily for Opera in IE it often looks different due to IE's poor compliance. The fact that most people (clients particularly, it seems) use IE as their primary (often only) browser compounds this.
The main reason I stick with Firefox rather than Opera is that this is what the Firefox bug tracking system looks like, and this is what the Opera one looks like - when something's not working and I'm sure it's not my fault I like to be able to read (and contribute to) a discussion about it.
Incidentally, one reason why I prefer Firefox to Chrome is that I spend a significant amount of time trying to do web development on trains with no network connection, and Chrome has this issue.
If you’re working on the front-line of web development you’d realise you don’t have the luxury of choosing the best browser. Corporates don't pay you build websites and intranets to browsers you like. The facts are simple, Windows: IE, Firefox MAC: Safari, Firefox. You can't support every browser unless specified by the client. Time costs money thus you need to select the most popular browsers on the most popular platforms. If any web developer had a choice, would they seriously support IE? It’s a simple fact of economics; it’s got nothing do with which browser is better.
Also Metropolis W3 School statistics are not a true representation of browser usage. W3 Schools visitors aren’t the general public, its techies. I’ve never seen a statistic before where Firefox is the number one browser? Obviously the general public have suddenly converted on mass to Firefox, interesting.
Opera, Chrome and IE 8+ all have good development tools built in to them; I think that the days of saying that Firefox is the best because of Firebug are mainly over.
Firefox still does have the most mature eco system of extensions. I do most of my development in Google Chrome nowadays, but there are still a few tasks, like managing Amazon servers via ElasticFox, that I find myself doing in Firefox. (Chrome's catching up on the extension front; Opera and IE still lag behind.)
Also, a comment on some of the other answers: there's a big difference between the browsers you test in and the browser you spend time in when you're developing. You should absolutely be doing testing and QA in every browser that you possibly can (I have a virtual machine or two running with various versions of various browsers installed). But there's no reason to be masochistic and spend your time developing in a browser that you don't like; if you find yourself running into too many surprises when testing, you probably need to improve your code, rather than switch the browser you're developing with.
But if I need to debug something DOM related (CSS, JS) I switch to Firefox, using Firebug. Opera's developer tool "Dragonfly" isn't only much to slow, but it also connects to an Opera server each time I open it, this is a pain.
I'm using constantly Opera, Safari, Firefox and Chrome for web development (switching each two-three days). It helps me to find early browser specific issues.
As of Opera, things are getting better. For example even a year ago I won't advice anybody use Opera ad main development browser. Nowadays now Dragonfly looks pretty mature.
But I still belive that firefox is most comfortable tool.
Chances are, you have a list of browsers that the site needs to work "correctly" in.
And chances are, Opera is not on that list (I've never had a client ask for it - I'm not sure I've ever had a client that would even have heard of it).
So, using Firefox for development generally means "develop in Firefox, then test in IE and Safari". Using Opera would mean "develop in Opera, then test in IE, Safari and Firefox." Just means more work for you to do.