In a follow-up to this question I've begun pondering what the most-relevant browsers of 2009 will be. I tend to determine relevance by the question "Is this browser cost beneficial to us supporting it" being answered by a significant number of developers and corporations.

For example, I would probably rate the current, 2008, list as follows (in order of cost-benefit):

• IE 6
• IE 7
• Firefox 2
• Safari 2 & Safari 3 (tie)
• -- common cut-off point --
• IE 5.5
• Opera 9.2

Starting in 2009 I predict that the list will be similar to the following:

• IE 7
• IE 6
• Firefox 3
• Safari 3
• -- common cut-off point --
• Opera 9.5

Not a whole lot changed, but a couple points to consider:

• I wouldn't be surprised if the switch between the dominance of IE 6 and IE 7 finally occurred.
• Firefox 3 will probably be released late spring/early summer - thankfully uptake will be fast (as it has, generally, been with past versions).
• Safari 3 is already shooting way up, Safari 2 will be a thing of the past come 2009.
• Opera will definitely have 9.5 out by then - maybe 10? Although, even if 10 is out, it definitely won't have a market share by next January.
• IE 5.5 will definitely squeeze out it's last remaining % into cost-benefit obscurity.

What's interesting about analyzing the cost-benefit of a browser is that it's done completely differently from straight-up analysis of browser market share. It's really a combination of market share and time that'll be spent customizing your application to work in that browser. Here's a quick chart to represent my choices:

The "Cost" is represented by the % of time that will be spent, beyond normal application development, spent exclusively with that browser. The "Benefit" is the % of market share that the browser has. Note that any browser that has a higher cost, than benefit, needs to be seriously considered for development.

What's interesting about this is that it use to be much-more clear-cut when choosing to develop for IE 6 - it had 80-90% market share so it's benefit was always considerably higher (or, at least, equal to) the time spent making it work in that browser. However, in 2009, that percentage will be considerably less (I'm estimating 35%, to IE 7's 45%) making it far less attractive as a platform. Note that Firefox and Safari, due to their less-buggy nature (and standards compliance) always have a higher benefit than cost, making them an easy target to work towards. Opera is problematic, however. It's, continued, low market share makes it a challenging platform to justify. It's for this reason that major frameworks, like Prototype, have ignored working with Opera up until this point - and understandably so.

Now it's not always a one-to-one trade-off in-between cost and benefit. I think it would even be safe to say that benefit is, at least, twice as important as cost. Ultimately, however, this depends upon the choices of those involved in the decision making and the skill of the developers working on the compliance. Is an extra 4-5% market share from Safari 3 worth 4-5 developer days? What about the added overhead to Quality Assurance and testing? It's never an easy problem - but it's one that we can, certainly, all get better at over time - but really only through hard work and experience.