Yes, it is possible. But, based on my testing, it's not likely.
What are these files?
During my tests, I was able to locate binary files in my Firefox profile directory at this path:
This suggests that the files contained therein are temporary files for asm.js. Information about these files is sparse, but this tweet from a self-reported Unity employee provides some substantiation (because Unity worked with Mozilla on game development with asm.js).
On my system, these names of these files followed the template
module<NUMBER>. While investigating the contents of these files, I was unable to find any likely passwords, even after registering for an account inside the add-on.
Where did these strings come from?
The strings you pulled from those files are certainly suspicious. I have been unable to recover anything similar on my own system, but there is another explanation.
The add-on includes Dropbox's zxcvbn library for calculating password strength. It is possible that asm.js attempted to optimize that code, resulting in password-like information being stored to your hard drive.
Using only words found in zxcvbn's dictionary, I was able to reconstruct some of the potential passwords you listed:
- monoethanolamine: mono + ethanol + a + mine
- monoethylamine: mono + ethyl + a + mine
The other passwords were likely generated using other rules (such as character substitution).
What can we conclude?
The files you found are most likely temporary files generated by Firefox. Specifically, when asm.js tries to optimize the zxcvbn code, it likely generates the temporary file containing some of the strings you found.
However, it could also be the case that the extension is using the zxcbvn wordlist to perform bruteforce attacks. A more extensive review of the code is needed to determine if that is the case.