Hi, I'm not familiar with Linux, but this shows you how to access Safe Mode with Fx closed Diagnose Firefox issues using Troubleshoot Mode

If that doesn't help; Refresh Refresh Firefox - reset add-ons and settings often fixes issues like yours, but before you do it I would backup your bookmarks or Profile, since it can very occasionally cause data loss. Open bookmarks > Show All Bookmarks > Import and Backup > Backup. Or, Export Bookmarks to HTML, and save them to a convenient location Note that Backup will overwrite any existing bookmarks when you restore them.

Back up and restore information in Firefox profiles

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Hi..Thanks for the assist. But, since the settings button don't work, i'd find it impossible to do most of what you said. Thankfully I had the foresight to partition my drive into 4 - 1 being just a storage where I kept stuff i want to keep. So I simply reinstalled Mint 18.3. Firefox works perfectly now. So I guess it had something to do with the system.

Hi, glad your fixed. Please mark your answer as the solution so others can find it.