Firefox can remember what you've entered in forms on web pages, also known as text fields. After you've entered something into a form on a web page (such as a search box), the next time you visit that page, your previous entry will be available to re-use. This article describes how to use the auto form fill feature and how to clear or prevent it from storing form entries.
To use your previous entry in a form:
If you want to remove one of your previous form entries from Firefox's history:
Repeat the process for each entry that you'd like to delete.
If you want Firefox to forget all of your previous form entries:
If you don't want Firefox to remember what you've entered into form fields, you can turn off the auto form fill feature:
Disabling form history also prevents Firefox from storing search history for the Search bar in the Navigation Toolbar.
If you find that Firefox does not save your form entries and you cannot re-use them, please read the article Firefox doesn't save web form entries.
Based on information from Deleting autocomplete entries (mozillaZine KB)
"Control whether Firefox automatically fills in forms with your information" is 74 characters long, including spaces. This article's title comes up truncated in search results. For example:
Google search: Control whether Firefox automatically fills in forms with your ... Yahoo search: Control whether Firefox automatically fills in forms with ...
What about dropping "with your information" from the title and rename it to this? Control whether Firefox automatically fills in forms
Any other suggestions?
For the release notes on version 38 there is a portion that is changed for both mobile and desktop that "autocomplete=off is no longer supported for username/password fields"
It might be worth mentioning this change here for questions about how users can turn on or off this feature. The only difference I see is wether or not the option to save passwords is on (maybe this should be added to another article instead like http://mzl.la/1BAQDYP or http://mzl.la/1xKrEoj)