I tested the new release on Ubuntu Linux 6.06 "Dapper Drake" on two machines. On the first machine, I moved my .mozilla directory so I could start with a fresh new profile; on the second, I left my profile in place. If you're going to test Firefox 2 Beta 1, it might be a good idea to back up your ~/.mozilla directory, just in case, so that your profile isn't corrupted if you decide to switch back to the Firefox 1.5 series.
Firefox handled importing the 1.5 profile just fine, and on the clean slate machine it offered to import bookmarks and settings from my Opera profile when it fired up for the first time. On the machine with the existing profile, Firefox checked all of the extensions I had installed, looked for updates for the extensions (none were found), and disabled the extensions deemed to be incompatible with Firefox 2.0.
The way Firefox handles extensions and themes has been streamlined in 2.0, so that you now have "Add-ons" instead of a separate manager for themes and extensions. It's not a major change from the 1.5.x series, and you still need to restart the browser to do something as simple as changing the browser theme. However, when you install a new extension or theme and restart Firefox, it "remembers" the session you had going and reopens all the pages and tabs that you had open when Firefox was restarted. This is also supposed to happen if Firefox crashes, but Firefox didn't crash while I was testing it.
If you've ever closed a tab without meaning to, you'll appreciate the new "Recently Closed Tabs" feature. Firefox tracks closed tabs and allows you to re-open them. This feature is in the new History menu (which used to be the Go menu).
Tab buttons now sport a "close tab" button by default, so you can just click on the red X on an individual tab to close it. If these features seem familiar, it's because they were available through Firefox extensions, but not part of the browser by default.
Firefox has a few new feed-reading features as well. When you click on an orange RSS button, Firefox will take you to a preview page of the site's feed, and you can subscribe to the feed using Firefox Live Bookmarks, Bloglines, Google Reader, or My Yahoo! I really like that Firefox is integrated with external services, and I hope that the Mozilla folks add a few additional options as time goes on.
The search box in Firefox has undergone a bit of renovation. When you start typing a search term in, it will provide a list of possible suggestions. For instance, if you use the Yahoo! search box and type "sha" you'll see a drop-down list that includes "radio shack," "shakira," "maria sharapova," and several other possible completions. The completions differ by search engine, and only the Answers.com, Google, and Yahoo! search boxes provide suggestions; if you're using the Wikipedia, Amazon.com, or Creative Commons search options, you won't see any.
The anti-phishing features aren't quite perfect yet. I went through my spam folder and tried some of the eBay, PayPal, and bank scams that I've received. Firefox warned me about phishing if a link was provided as an IP address rather than a typical URL, but I didn't get any warning when trying to connect to "http://rrcs-24-136-127-57.nyc.biz.rr.com:81/us/" when it was marked as "Click here to update your PayPal account information." I'd say Firefox was detecting phishing URLs with about 20% accuracy, and it missed several outlandish URLs. However, according to the project's notes, this is to be expected, and future versions of Firefox 2 should be more accurate in their diagnosis of phishing sites.
The beta also allows you to report phishing Web sites -- just click on Help -> Report Phishing Website. I'm not sure the Help menu is the most logical location for the feature, but at least it's there. When you report a phishing site, it's relayed to the Google Safe Browsing team, so it looks like the "detect phishing" functionality from the Google toolbar is being integrated into Firefox directly, or the Firefox team is using Google's API.
And Firefox might not be of any help at all with the new crop of phishing attempts, anyway. When I was looking through the phishing messages, I noticed a couple that had no links whatsoever -- just phone numbers to call, where operators are presumably standing by to fleece innocent users. As wonderful as Firefox is, users must still supply some common sense.
Just plain browsing
I spent a fair amount of time just running through sites I visit frequently, to see if any of the sites looked better or worse in the beta, or if they rendered more quickly or more slowly. I didn't detect any major changes. It seemed like the beta rendered sites a bit faster than Firefox 1.5.x, but I don't have any hard data on that.
I did notice that one site I visit from time to time, the Tapped Weblog, looked better in the beta than in Firefox 1.5. The sidebar ad on the left side of this page renders oddly in 1.5, obscuring the page's text, but it rendered just fine in the 2.0 beta.
Sadly, the new Firefox series doesn't seem to be any better at blocking pop-ups than the 1.5 series. I've noticed an increasing number of pop-ups that slip under Firefox's radar, and I was really hoping that this new series would take care of those. One example is the Quotes of the Day page, which inflicts a pop-up on you the first time you click anywhere in the page. I'm not sure if the Firefox developers have given up on the pop-ups arms race, or if they're just being skunked by malicious site owners; it seems like Firefox enjoyed a brief period of near-immunity to pop-ups, but I run into pop-ups several times a day now when using Firefox.
Just for fun, I checked the beta against the Acid2 Browser Test to see if it passed. Opera 9, Konqueror, and Safari pass the test with flying colors, but Firefox still doesn't. That's probably not a big deal, considering that Firefox correctly renders the vast majority of sites, but it would be nice.
Upgrades aren't all about new features, of course. The beta also removes one or two features as well, among them the ability to block images if they're not from the original Web site. I'm not sure if this is something that's going to be permanently removed, or if it's part of the development process, but I'd like to see that feature remain.
A few of the tab options have been removed as well. In Firefox 1.5.x, you can direct Firefox to open links passed by other apps in a new window, new tab, or open the links in the most recent window/tab available. The beta removes this setting from the tab preference dialog altogether.
If Web browsing is "mission-critical" for you, or if your favorite extensions don't have support for the Firefox 2 series, wait until the 2.0 final release before upgrading to Firefox 2. From the testing I've done so far, though, the beta is stable enough for day-to-day use, and the tab and feed-reading features might be compelling enough for you to start running the 2.x series full-time right now.