Hello rchevat, I think I do have a solution to your problem. The problem could be because you have to much cache filled up in Firefox. Pressing Ctrl+Shift+Delete at the same time should bring you to a page that says "Clear Recent History" You can change your time range to delete depending on what works and whatnot (below I have an example image) . I recommend checking all the boxes as that will not effect your passwords, addons, etc. Tell me if that helped and Stay Safe!

You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Options/Preferences).

"Remove the Cookies" for websites that cause problems:

• Options/Preferences -> Privacy & Security
  Cookies and Site Data: "Manage Data"

"Clear the Cache":

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Clear Data -> Cached Web Content: Clear

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

I was having a problem with my RogersBank MasterCard log-in page which I had used with no issue for year. After a recent Firefox update when I clicked on the sign in page it would load blank.

I simply held the Shift key and clicked the reload button and it now works no problem.