Hello, you may have session restore issues. Can you try this?

• Configuring session restore

Make sure you close Firefox (Firefox -> Quit) with all windows you want to restore still open.

Make sure you do not run Firefox in permanent Private Browsing mode (Always use Private Browsing mode; Never Remember History).

• https://support.mozilla.org/en-US/kb/Private+Browsing

• Options/Preferences -> Privacy & Security -> Firefox will: "Use custom settings for history"
• remove checkmark: [ ] "Always use Private Browsing mode"

In case you use "Clear history when Firefox closes" or otherwise clear history.

• do not clear the Browsing History

• Options/Preferences -> Privacy & Security -> Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an "Allow" exception you may want to keep

Thanks for the responses. I feel like an idiot though as it now seems to be working and I haven't changed anything (maybe there was some other conflict?). Anyway it seems other people may have had this problem and have benefited from your answers. Cheers