There are many missing, I am only posting the ones related to web development:

1-) DarkReader (protect your eyes while working at night)

2-) SimilarWeb (site rank)

3-) IPWhois (registrar and IP info. Some other useful stuff too)

4-) BuiltWith (how can this be not on the list?!)

5-) Seo Analysis by WooRank (good detailed SEO stuff)

6-) Web Developer by Chris Pederick (disable js and other mods)

7-) StyleBot (edit and override CSS)

8-) TamperMonkey (Inject JS. I can't live without this and I already have over 30 scripts running)

9-) Edit this cookie (cookie editor, very useful and detailed cookie info)

10-) Clear Session (deletes per-site session info)

11-) FireShot (screenshot)

12-) MousePinchZoom (desktop mouse zoom function instead of scaling the screen. Very useful for development for checking the elements up close)

13-) Word Count (count selected text word count, useful for article SEO related stuff)

I have more semi-developer ones that are not listed here. I really use these on a daily basis and removing any would disrupt my workflow.