Nothing's wrong with Firefox except that it's got poor marketing. Google is hyping Chrome, and Google has the biggest soapbox on the web to shout from. Firefox has/had a strong start based on functionality, but marketing visibility is inevitably going to eat away at the lead.
That is just simply not true on all fronts. Firefox has had far, far
more marketing than Chrome (huge community campaigns, media stunts like setting the dubious "record" for software downloads, competitions by firefox fans to see who could evangelize it most...). It's simply not even close, and Google doesn't push Chrome very hard (and Google used to push firefox and even pay webmasters when they got others to download it).
It's also not true that there is little difference but marketing. Chrome simply stands head and shoulders over Firefox in many objective measurements such as:
- Resources used
(doesn't leak memory like sieve like Firefox)
The security model is superior to all other browsers on the marketplace, the UI is a dramatic improvement in usability over all other browsers, and the resource use model (each tab is separate from others so it can crash just a plugin, or just a tab without crashing the whole browser) is a breath of fresh air for heavy internet users.
The bottom line is that Google built the best browser on the complacent marketplace just like Firefox once did and just like Firefox will now have to get back to doing if it wants to keep its browser share.
Google is a big leader in these heavy web apps (Gmail, Google Docs, Google Reader) so a faster internet is a benefit to them and they simply made a browser that blows firefox out of the water. The performance improvement is as dramatic as Firefox's improvement over IE was if not more so.