I found a simple solution (Mac) that I didn’t see mentioned anywhere else. This solution should hopefully work if your MetaMask is blank after your computer crashed. Here are the steps:
Solution:
1. Find your local metamask extension folder
Should be here:
/Users/{your-username}/Library/Firefox/Profiles/{your-profile}/storage/default/moz-extension+++{extension-uuid}^userContextId=XXXXXXX
{your-username} is your computer username. {your-profile} is your Firefox profile. To find your extension-uuid paste about:debugging#addons into your address bar and scroll down until you see MetaMask. The UUID will be labelled as Internal UUID.
2. Locate the file whose name is a number
Inside the extension folder there will be another folder called idb and inside that folder is another folder named something like 3647222921wleabcEoxlt-eengsairo.files. Finally, inside that folder is a file whose name is a number (1 or 2 or even 3020). Mine was called 3039 and was ~300kb in size.
3. Make a copy of this file
Copy this file and increment the name by 1. So in my case I named the copy 3040. If your file is 58 name the copy 59.
4. Restart Firefox
Fully restart Firefox (press the command and Q keys together to properly quit the application).
5. Open MetaMask
Now just open MetaMask and it should be working again. If not, go back to step 3 and increment the copied file name again and restart Firefox again. In my case I would rename my copied file from 3040 to 3041.
Explanation
So it turns out that every time you open Firefox this file’s name is incremented by anywhere between 1 to 10 (the next time I opened Firefox my file was renamed from 3040 to 3048). This file name is stored in the .sqlite file found in the parent folder of the file and if your computer crashes these might get out of sync. In my case the file was named 3039 but in the .sqlite file it was referenced as 3040.
I’m not an extension developer so I am not sure if this is a Firefox quirk or if it’s a MetaMask quirk.
I hope this helps anybody facing this issue!