Firefox's download window can sometimes be awkward, especially for people who like to do all their browsing in only one window. And, considering the default behavior of the Windows taskbar, to group all your windows under one icon and Mac OS X's dock which makes using multi-windowed applications kind of painful, restraining yourself to a window per application seems like the obvious thing to do in this day and age.
There are some add-ons that put your downloads in a tab (Opera style) like Downloads in Tab and I strongly believe that eventually Mozilla will make this a core Firefox feature.
Since Opera first introduced their Speed Dial page, other browser makers integrated this feature into their products in various forms. Chrome developed the idea by introducing web apps and the most visited pages into the picture and for all other browsers there had been a flurry of extensions that more or less did the same.
A lot of people had a problem (and some still have) with Firefox 4+'s interface. "Chrome knockoff" and "dumbing down" are two terms that you might see pop out in internet discussions about Firefox's current interface. While I think the current UI is not that bad because it saves some more space and thanks to its minimalist style lets you focus on the job at hand, I understand and sympathize with people wanting to turn back the hands of time and return to the good old trusty Firefox 3.6.
After a little more than a year from Firefox 4's release on March 22nd, 2011, Firefox 3.6 will cease to be updated anymore. Some users still hold on to this version in protest of Mozilla's interface changes and rapid release cycles as well as extension breakages. While the "interface changes" issue is highly subjective and can be resolved in one minute with a theme, the other two issues are becoming less and less relevant as time goes by.
The problem was that before 4.0, add-on developers expected major Firefox releases every one or two years and planned their development accordingly, tying their add-ons to specific versions. When major releases started coming every 6 weeks, there were a few months when a lot of extensions broke. Mozilla was reasonably quick to step in and create an internal tool that would automatically analyze extensions and mark them as compatible with newer versions if that would be the case.
If you use a lot of tabs or if you do a lot of stuff at the same time, sooner or later you'll feel that the tab bar is not big enough. Luckily, Firefox has a great way to organize your open tabs called Tab Groups (also known as Panorama). We've made a video tutorial to teach you all you need to know about it.
After a lot of speculation, Mozilla has announced that it had struck a 3 year deal with Google for the default position in the search bar. Rumour has it that the spot was also sought after by Yahoo and more importantly by Microsoft for its Bing search engine. Interestingly enough, a couple of month ago, Mozilla and Microsoft announced a Firefox with Bing edition, which a lot of people thought would pave the way to a multi-year deal similar to the one Firefox had with Google at the time.