Mozilla is ditching visible version numbers
Loads of moans about the version number I see, despite the major version of Firefox meaning nothing after version 4 was released. In fact, Mozilla is going to remove visible version numbers from its products shortly - look at the download page for Thunderbird at http://www.mozilla.com/thunderbird/ for example.
It's funny how no-one has mentioned the same thing happens with Google Chrome - they version inflate at the same rate: now at version 13 - 7 ahead of Firefox!) and yet what they sneakily do is silent updates (service in WIndows, at job in Linux) and never tell the user they've got a new version. I suspect Mozilla are preparing to do something similar soon with their products.
Also note that Firefox 3.6.X is sort of becoming a long-lived version (yes, it just got another minor uipdate) - something that Google haven't bothered doing at all with Chrome.
The extension version checking is an issue - but once I got everything sorted in Firefox 4, versions 5 and 6 haven't caused me any problems. There is the Add-ons Compability Reporter extension, should you need to override the version check (no idea if Chrome does any similar thing - do they even version check or just leave extensions to break?).
I think one way that users could have been appeased was if Firefox numbered itself with a reverse date format (20110801 or something) - then there's no major version field for people to gripe about.
The worst thing for me with Firefox 6 was the terrible copycat of the stupid URL domain highlighting (about:config, search for "formatting" and double-click it to set it to false to fix this idiocy) - lets show the domain name in normal text and grey out every other remaining character in the entire URL to make it unreadable. Why not bold or colour the domain name and leave the rest of the URL in a normal font/colour? A dumb copy of Chrome/Opera's awful display of URLx and not a clever move at all.
In conclusion, Firefox 6, like version 5, is a relatively minor August 2011 update. The next update (yes, version 7, though I reckon "Sep/Oct 2011" would be a more appropriate version string) will start to see both memory and performance improvements for Firefox and I think that release will be a lot more "exciting" for end-users. Rumours have it that update after that (yes, 8 I suppose) will be very good w.r.t. memory usage in particular - it may beat all the other browsers w.r.t. memory usage/management. It may even bring some ex-Firefoxians back into the fold again...