One reason why I stick with Firefox is because of its capabilities to expand its features with a wide range of optional extensions or adds-on. Customization, is the power of Firefox. People can do extensive customization on Firefox user interface via extensions. Firefox has many extension useful for web development.
Here is my top ten Firefox extensions I mostly used for developing a website :
I do believe there are many alternative to the list above, but those above are I personally currently use. If you have any other extensions worth to replace those above, let me know.