If you're new to MetaMask or just the whole managing your own keys thing in general and have put in more than you can bear to lose, then this a friendly reminder to backup your MetaMask account and wallet so that you can load it in another browser.
There are two components to it.
Export you account's private key. Click the three dots and then on 'Account Details'. Then click on 'Export Private Key'.
Click on your display picture and then on Settings. Go to security and privacy and then click on 'Reveal Seed Phrase'. Save the seed phrase somewhere secure.
Congratulations. You have backed up your MetaMask account and wallet. If you have a spare laptop, i'd encourage you to test it out by importing your account.
Shit happens when you least expect it. Better back it up early!