You've already told Firefox not to save passwords and logins, but you've noticed it still keeps trying to auto fill forms for you. Don't worry, there's an easy fix for this. The solution is not obvious at first glance, but rest assured it's fast and simple:
Step 1: Go to preferences
Go to the preferences menu in Firefox - click on the symbol with the 3 lines as shown in the image, then click on "preferences":
Step 2: Go to "Privacy and Security" and then "History"
Your History settings will initially say "Firefox will Remember History", but you need to change this to "Use custom settings for history" as shown below.
Assuming you've completed the above, you just have one final step to finish up with.
Step 3: Uncheck "Remember search and form history"
At this point, you'll see a new series of checkboxes appear. One of these is "Remember search and form history". Uncheck it. That's it, you're done!
To sum up, your preferences for history should now match those in the image below. Problem solved: Firefox will no longer auto fill forms for you.
The illustrated tutorial above shows you how to stop Firefox from automatically filling forms for you. Oddly enough, it's a separate setting to filling passwords or login names, so the auto form fill setting is actually quite hard to find if you don't already know about it. We're hoping this is something that Firefox might consider changing in subsequent versions of the browser. Most people who are privacy-conscious don't want to have to hunt around for where to stop the auto fill for forms. Considering that Firefox is a privacy-oriented browser, it really ought to place the option for autofill of forms in a more prominent place.
It's also odd that autofill for searches is bundled together with autofill for forms as one option, which is rather a blunt instrument. Most people are seeking only to remove the form auto fill, but not necessarily search auto fill. Furthermore, form autofill in Firefox ought to be placed along with the options to save logins for websites, or else alongside the option to autofill addresses (an oddly specific option!)
To sum up, it's not clear why Firefox has set up auto fill options to be so hard to find, but on a positive note, at least it's easy to turn off, as illustrated above.