What are the sites when you do that so others can test if that is happening or not.

hi, would you be able to capture and share a performance profile while this problem is happening?: https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Reporting_a_Performance_Problem

Here is my performance profile for when this happens https://perfht.ml/2m9E9aM. I noticed it happens more often when I am trying to open youtube but it happens with other websites sometimes also.

You can check for problems with the sessionstore.jsonlz4 file in the Firefox profile folder that stores session data.

• delete sessionstore.jsonlz4 and sessionstore.js

When sessionstore.jsonlz4 is deleted you lose pinned tabs and open tabs and you will have to recreate them, so if necessary make a note or bookmark them.

You can check for problems with the places.sqlite database (bookmarks and history) in the Firefox profile folder.

• use "Verify Integrity" on the "Help -> Troubleshooting Information" (about:support) page

If "Verify Integrity" on the "Help -> Troubleshooting Information" (about:support) page cannot repair places.sqlite then remove all places.sqlite files in the Firefox profile folder. Firefox will rebuild places.sqlite and restore the bookmarks from a recent JSON backup in the bookmarkbackups folder.

• keep a backup copy of places.sqlite in case a new places.sqlite database has to be created
• http://kb.mozillazine.org/Unable_to_process_the_backup_file_-_Firefox

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

I deleted sessionstore.jsonlz4 and verified integrity without deleting places.sqlite. So far it looks like it has worked. Thanks for your help.

thanks for providing a performance profile. do you have any recently submitted crash reports (starting with bp-) listed when you type "about:crashes" into the address bar? if yes, could you please post the handful of their most recent ids as well?

I have one submitted crash report, all the others are unsubmitted. https://crash-stats.mozilla.com/report/index/bp-590affc9-a943-4ab9-b039-52b311180510