I took a screenshot of the missing button in firefox.

I think that the reset button is only available (enabled) if you have started Firefox with a profile that is registered in profiles.ini (i.e. this profile is present in the Profile Manager) and a profile migrator is available.

• https://dxr.mozilla.org/mozilla-release/source/toolkit/modules/ResetProfile.jsm

Do you have specific reasons or issues that you want to reset Firefox and create a new profile? Also see the about:profiles page for all registered profiles.

Slow and laggy, i think i got something on firefox, because the whole browser is temporarily frozen for 10 or so seconds when i launch it, it was smooth in the past.

Also get random moments where firefox is lagging.

I deleted .mozilla, it fixed the lag. Not sure how, but firefox is better now.

You can always use the Profile Manager to create a new profile. Using the Profile Manager allows to switch back and forth between profiles or use the about:profiles page. See this article about how to transfer personal data.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

Note that there is a secondary location used for temporary files.

• ~/.cache/mozilla/firefox/