Hi Dandelion, you can install a different version of Firefox into a separate directory, but there is some danger that it will upconvert your Firefox 52 profile when you start it up, making it permanently incompatible with Firefox 52. It's a little bit complicated keeping them from stepping on one another. Here are my general thoughts, but you might seek out other comments as well.

(1) Make a backup! Back up and restore information in Firefox profiles

(2) Create a new profile (let's call it Fx78 for the moment) and make it the default -- this should get upconverted without disturbing your old profile, or it will be ignored and end up being extra (steps below).

(3) Do a custom install of Firefox 78 into its own program folder and let it take over the new profile or create its own.

(4) Update your Firefox 52 shortcut to specify the applicable profile, or to point to the Profile Manager dialog.

Step #2

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

Click the "Create a New Profile" button, then click Next. Assign a name like Fx78, ignore the option to relocate the profile folder, and click the Finish button.

Scroll down to that profile and if you see a Set as Default Profile button, click that to make it the default.

Step #3

See: Custom installation of Firefox on Windows. Short story: you need the "full" installer which lets you specify the folder.

Step #4

You can set the old Firefox shortcut to use a specific profile or call up the external Profile Manager by modifying the "Target" field.

Right-click a desktop shortcut and choose Properties. If you pinned the shortcut to the Task bar, right-click the icon, then right-click Mozilla Firefox to get to Properties.

Windows should show the Shortcut tab automatically, or click it.

The Target line usually will have something like:

• "C:\Program Files (x86)\Mozilla Firefox\firefox.exe"
• "C:\Program Files\Mozilla Firefox\firefox.exe"

Add a space and -P to have the shortcut call up the Profile Manager so you can select the old profile from the list. So

• "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -P
• "C:\Program Files\Mozilla Firefox\firefox.exe" -P

If you know the name of the profile -- for example, if it's default -- then you can add that to the shortcut as well. For example:

• "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -P "default"
• "C:\Program Files\Mozilla Firefox\firefox.exe" -P "default"

Disclaimer: I can't give guarantees that this will all work, so don't forget step #1 -- make a backup.

Regarding Flash, your bank must be planning to update its site. Adobe has announced there is a kill switch in the Flash plugin that will make it inoperable on January 12, 2021.

You can also rename profiles.ini to make Firefox 83 create a new xxxxxxxx.default-release profile and lock that profile for Firefox 83. Then you can start Firefox 52 with the Profile Manager (add a space and -P to the target line) and re-register your previous Firefox 52 profile by using the "Choose Folder" button. See:

• https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

Best is probably to use a desktop shortcut that specifies the profile folder (-P "<profile>"), at least for Firefox 52.

• https://developer.mozilla.org/en-US/Command_Line_Options