There were no UI changes between 5 and 6.
Corrected that for you 
By the way, currently have 4 tabs open (3 this site and 1 wikipedia) and FF is using 370MB of RAM according to task manager. Not very impressive.
whats funny is its clear the dev's are aware of the huge ram leak issue on ff4, as they did a plaster fix on 5 and 6.
On ff4, the ram usage just keeps going up whilst its idle, it keeps going up until you do something like close the active tab or load a new page in that tab, at which point the ram will go back down again (not necessarily all of it but most of it).
On ff5, the same happens but they added some kind of process to it that at intervals flushes the data out of ram so it will keep going up then after say 30 seconds it goes back down again and thn will start going up again and then another 30 seconds or so later it recovers again, so its up down up down, so intead of fixing the actual leak they added a mechanism to flush it at set intervals.
ff6 the same as ff5 except it seems to leak a a higher rate.
the about:memory page shows the leak is in the javascript heap allocation.
It would seem the stuttering issues are not fixed at all in ff4,5,6 I just thought they were as I was until very recently only loading a dozen or so tabs in the browser at once. Plus to make matters worse changes were made in 4 upwards that have broken bartab and even to the point the dev of bartab cant update it to work fully on 4,5,6. I feel the core causes of firefox's stittering are.
1 - storing data in sqlite format, this is significantly slower than plain text storage or using the registry. Data gets flushed to these files at regular intervals hence the stutters.
2 - frequent garbage collection, this is frequent I assume due to lots of memory leaks, IE also has memory leaks but it doesnt seem to bog down the browser like it does on FF.
3 - garbage collection, browser gui, web site data all sharing a single process, so this means all tied down to one cpu core for performance and using loads of ram in one process. So eg. if you have IE9 open with 10 tabs, you will probably have 4 or 5 iexplore.exe processes splitting the cpu/ram load between them and if a tab crashes only the tabs sharing that single process crash with it, not the entire app. firefox will have the entire lot in one firefox.exe process, except if the plugin-conteiner is enabled (mentioned few posts back) then things like flash will go in an extra process which stops flash stuttering due to GC.
4 - no sandbox, in 2011 this is just silly to not have a built in sandbox function, even IE has had it for many years now since vista launch. chrome had from start.
there is a few other things but on these basics firefox is seeing next to no progression from ff3.6 to ff6. On the ram load/leaks, stuttering its actually regressed.
If we compare the progress of IE7 to IE9, microsoft seem to have worked on their main issues. They massively improved compliance to standards, IE9 is very good on it. They improved speed, IE9 is my fastest browser easily, way faster than FF6. They improved security, sandboxing, built in ad protection, built in activex protections, and they added built in crash protection. They also will support IE9 until about 2016/2017 rather than a 6 week EOL from firefox.
Edited by Chrysalis (Sat 27-Aug-11 08:41:50)