Take a good look at the privacy policy before you install this! Please note that you are also giving privacy permissions to this app related to Google and related to LogMeIn.com
All of this looks legitimate. However, as with Google and Facebook, LogMeIn seeks to combine information collected through the app with information about me which that company will collect FROM OTHER SOURCES. Even if it's mostly for app functionality and marketing purposes. I don't need any more advertising or spam than I already get!

See for yourself:
https://addons.mozilla.org/en-US/firefox/addon/lastpass-password-manager/privacy/

This add-on doesn't stay with Firefox. Every time I open Firefox I have to re-download LastPass.

Works as advertised except one: I have 2FA activated and I am infuriated by constant re-authorization prompts, despite ticking to remember the browser. I am nagged at least once a day on all my browsers.

Doesn't remember masterpassword or remembers 2FA for 30 days when I check the box. This fails in Firefox for over one year now and doesn't get fixed.

Please fix the Android Extension. When you type your password and try to login nothing happens.
It would be a lot better to have the Firefox Mobile Extension working because the LastPass App is just not reliable in recognizing logins

Fantastic when it works, but it stops functioning properly every few weeks. I need to remove the extension and reinstall to get it working again.

tldr: It can be really useful but also super frustrating when you run into bugs.

This service is a blessing and a curse. When things go well, I love it. It makes everything a breeze. I know that my passwords are much more secure, and it is well worth the price.

On the other hand, when things go poorly, and it doesn't save the password, and then deletes it from your clipboard at a really crucial moment, it can be really frustrating. While that can be avoided by being extra cautious and while I was able to eventually find the history of recently generated passwords, it can still cause a ton of frustration.

Another big issue is when the extension occasionally bricks the entire browser for up to a minute. When the icon is yellow, I avoid clicking it like the plague.

With these factors, I came to the conclusion of a 3.

not loading in latest firefox

Used to work great, now it wont load or fill in anything