Firefox has been doing well for quite some time, in some regions of the world better than others. Where it is doing supremely well is Europe, with a massive 35% market share
for its latest version alone, making it the biggest region by percentage for the browser worldwide. Certain countries have even higher figures, but 35% for the entire region is impressive.
It is interesting to see how a browser's adoption rate can be affected so much by the region it is in. South Korea, for instance, still relies almost exclusively on Internet Explorer, which makes up almost 99% of browsers locally. Firefox, Chrome, Safari, Opera and all other browsers combined barely amount to 1-2%. Then you have the complete opposite in Europe, where the Firefox market share taking into account all versions is now only 10% behind Internet Explorer.
On a global scale, Mozilla is still doing well, proving that the world doesn't have to tie itself to IE and that they can compete well enough on their own. So is Microsoft in trouble? It'll depend on what they plan to do going forward. It's easy to criticize them for what they have done in the past with the still most-popular browser, but what will truly matter is how the web changes and what they do to adapt. Streaming video and social network integration were not goals of browsers at first. In just a few years the market may be vastly different from what it is today and Microsoft sure has the resources to invest in the future of its browser.