Can you provide the steps to replicate the issue? What are the sites? Do you have the same issue with other browsers? Have you tried the same steps in safe mode?

How many tabs have you open< just a few (in the tens) or quite a lot (in the hundreds) ?

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. sessionstore.jsonlz4 is only present in the Firefox profile folder when Firefox is closed.

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 Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

just have 4-5 tabs open and doesn't seem to happen in Chrome. I cleard the cache and the history and everything else but.....