In the last round of changes from Slackware, Firefox 3 has been replaced with Firefox 4. This has brought some good, and some bad.
First of all, I have lost the Firebug add-on. I use this all the time for web development, so it's a serious loss. There is active development on Firebug and it looks like a version for Firefox 4 will soon be available. I'll wait a little bit to see if Firebug gets a quick upgrade, but if it doesn't, I will have to go back to Firefox 3 until Firebug upgrades.
AdblockPlus still works and I really can't work without that, so that's good.
The physical layout has changed.
I have lost the reload and stop buttons on the toolbar. They moved instead down to being small buttons to the right of the URL. This seems strange, and I don't see any benefit from it, but at least I can still stop and reload.
The tab titles have moved above URL and search bar. Strange, I don't see any benefit, but then I don't see anything wrong with it. I don't really care about this one. But I just looked under View -> Toolbars and there's an option to put the toolbars on top. This may have been here forever and I never noticed it. I set the option off so things go back to what I am used to.
There is no longer a status bar at the bottom of the screen. I used this to show the output of a couple of small add-ons, but now that output is gone. I should delete those add-ons now. I would use it mostly to show the URL for links when I hovered over them. I can still hover over the links and have the URL shown in the same place, but it overwrites the bottom of the contents of the page. No big deal, I can live with this. It makes me appreciate web pages that put a footer that is always wedged against the bottom of the screen.
There is one behaviour with tabs that has changed that I totally love. I used to get irritated with one tab behaviour, and now my irritation is gone. If I had a bunch of tabs open, and the middle one was a page with a lot of links (I'm talking Reddit here), I used to middle-click on the links, and a tab would open up to the right with the new page. I would view the page and then close that tab. Focus would switch to the tab to the right, which is not what I wanted. I wanted it to go back to the tab with Reddit. Well, this has been changed in my favour. It's not as simple as closing a tab and focus shifts to the tab on the right. That still happens. I don't know the specific algorithm, but if I spawn a new tab, then view it and close it, focus shifts back to the tab that spawned it. That's roughly what I have discovered, and it's a change that favours my browsing habits, so I am very pleased with it.
Update: you have to close the tab within a short period of time for it to go back to the tab that spawned it. This is very sophisticated behaviour and I haven't figured out all the rules yet.
Flash crashes all the time. If I watch a YouTube video, it plays and stops and if I come back a little later to that same tab, I see that Flash has crashed and there is a nice notice about it. I can reload the page and it will start again. Maybe this always happened like this, but the crash wasn't obvious before and now they have made it obvious.
Firefox 4 looks a little slicker, and seems a little faster, and I probably have a lot more discovery to do.
But I have to weigh up the loss of Firebug against the better tab habits, and choose soon. Which benefits me the most?