The Extended Support Release of Firefox 115 is the last Firefox version for MacOS Mojave ([[Firefox users on macOS 10.12, 10.13 and 10.14 moving to Extended Support Release]]). There's no need to reinstall; that won't help. So that leaves a few other options: (A) Upgrade to a newer version of MacOS, if your computer supports it. (I collected these links in December so it's possible there is something newer already.) You might need to use Safari to get the most accurate compatibility check. * Monterey (12): https://apps.apple.com/us/app/macos-monterey/id1576738294?mt=12 * Big Sur (11): https://apps.apple.com/us/app/macos-big-sur/id1526878132?mt=12 * Catalina (10.15): https://apps.apple.com/us/app/macos-catalina/id1466841314?mt=12 * Apple support article: [https://support.apple.com/en-us/102662 How to download and install macOS] (B) Set Firefox to lie to the site about what version of Firefox you have and hope that doesn't create an incompatibility. If you want to try it: ''(1)'' In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. ''More info on about:config:'' [[Configuration Editor for Firefox]]. ''The moderators would like us to remind you that changes made through this back door aren't fully supported.'' ''(2)'' In the search box in the page, type or paste '''forceVersion''' and pause while the list is filtered ''(3)'' Double-click the '''network.http.useragent.forceVersion''' preference to display an editing field, and change the value to '''128''' then press Enter or click the blue check mark button to save the change. If you try the problem site again in a new tab, does it still give you the same message, or does something else happen now? (C) Use Safari or another browser for that site.

Jacob, My apologies. I did not know that anyone had responded to my question until I came back to check the post today. With the version of OS I'm running, Firefox is my only option for secure financial sites. Everyone else (Safari, Brave, etc.) have stopped updating. But it's good to know I have the latest version of Firefox. I don't understand why it wanted me to upgrade to the same version, but you solved my question. Thank you!