One of Firefox's most popular features is its add-on support, with its accompanying deep add-on catalog. The new Firefox 4 Mobile for Android (download) and for Maemo devices (download) also support add-ons, so we've got a collection of Firefox mobile add-on essentials for you that covers the bases, from useful ad blocking to interesting, mobile-specific password helpers.
The best-known add-on that's a must-have is Adblock Plus (download), ported by the developer from Firefox desktop to mobile. If you're not familiar with it, it blocks ads by using blacklists to filter out the ads. Once installed, the extension guides you to a list of filters you can install. It will recommend a filter based on which country you're in. If you do want to see ads on a particular site, you don't have to uninstall the add-on. Tap the favicon of the site you're on and an option will appear in the drop-down to toggle ad blocking for that site.
Another good mobile security extension is Less Spam, Please (download). It creates a partially randomized e-mail address that's both disposable and reusable, thus keeping your primary e-mail free of potential spam and clutter, and lessening the likelihood that your main account will get hacked. The add-on relies on Web mail services like YopMail, MailCatch, Humaility, or Mailinator to create the e-mail address on the fly. Then, until you delete that account, your log-in to that Web site is associated with the new dummy e-mail.
Other mobile add-ons focus on Web site access and readability. URL Fixer (download) autocorrects common typos in the URL bar, so that when you type ".cmo" it knows you meant ".com". There's an option in the add-on to have it ask you to confirm autocorrections before applying them, providing a level of protection against improper autocorrects.
The add-on Bigger Text (download), perhaps unsurprisingly, makes the text of the Web site you're viewing bigger, and it does it in two different ways. In the add-on's Options menu, you can set a new default font size larger than the standard one. It also adds a "Bigger Text" button to the site menu, accessible by tapping the site's favicon. Tap the Bigger Text button and a site's font automatically gets bigger.
Based on the code that powers Readability, Reading List (download) lets you save pages to read for later. It adds a book icon to the toolbar (viewable when you drag your finger from the right edge of the screen to the left), and a Save for Later option to the site menu. Tap the favicon and then the Save for Later button to save a page, and tap the aforementioned book icon to access your sites.
Personally, I find this a bit superfluous to just using the bookmark star, but I know that a lot of people like the Readibility-style features and separate organization of sites to read later from their regular bookmark lists.
There are some excellent add-ons to extend Firefox Mobile's feature set, too. Phony (download) lets you fake a browser's useragent header, which is the piece of code that Web sites use to determine whether you see the mobile or desktop version of a site. This can be useful if, for example, you want to see the Mac version of Download.com instead of the mobile version.
Mobile Profiles (download) is a simple little add-on that helps you create multiple browsing profiles in Firefox Mobile. This could be very useful for families and other people who share devices, so that each person's browsing information is kept separate. Meanwhile, Lazy Click (download) could wind up being a sleeper hit of an add-on. It fixes missed screen taps by applying them to the closest clickable link or button. The options let you customize the radius of error, and users who've found their Android touch screens to be inaccurate are likely to get the most out of this.
Got a favorite Firefox 4 Mobile add-on that I didn't mention here? Tell me about it in the comments below.