There are plenty of Firefox plugins that help make the day-to-day tasks of a web developer a little bit easier.
Here are 11 of my favorites....
When working with multiple people on projects, using screenshots as part of the feedback process is extremely helpful. FireShot streamlines this and enables you to take screenshots of pages and quickly insert text and graphical annotations.
Web Developer 1.1.6
This is another add-on with useful debugging tools.
Another handy tool for web developers, this add-on makes it simple to work with the DOM inspector.
Execute JS 0.2.1
Cookie Watcher 0.9
For developers who develop web applications that rely on cookies, Cookie Watcher makes it quick and easy to track a specific cookie as you test your applications.
Working with CSS is a bit less tedious with this CSS property viewer.
Cache Status 0.7.3
Easily manage your disk and RAM caches with this add-on.
Firefox Accessibility Extension 188.8.131.52
If you need to test your websites for accessibility features designed to assist people with disabilities in their browsing, the Firefox Accessibility Extension can be helpful.
Need to compare the HTML code between different versions of your pages? PageDiff makes doing that simple.
This is a very cool add-on that lets you see the HTML blocks for a specific part of a page just by moving the cursor over the area whose HTML you want to view.