I just opened the newsletter template with no issues. see screenshot Can you provide steps to replicate the issue? Can we access the same file(s) that are crashing on you? Which mac os? Do you have the same issue with Firefox in Troubleshoot Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf

Did you try clearing the browser cache? https://support.mozilla.org/en-US/kb/how-clear-firefox-cache#

You can Refresh Firefox. https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

We're sorry to hear that Firefox is crashing. In order to assist you better, please follow the steps below to provide us crash IDs to help us learn more about your crash.

The crash report is several pages of data. We need the report numbers to see the whole report.

1. Enter about:crashes in the Firefox address bar and press Enter. A list of Submitted (and Unsubmitted, if any) Crash Reports will appear, similar to the one shown below.
2. Copy the 5 most recent Submitted Report IDs that start with bp- and then go back to your forum question and paste those IDs into the "Post a Reply" box.

Note: If a recent Report ID does not start with bp- click on it to submit the report.

(Please don't take a screenshot of your crashes, just copy and paste the IDs. The below image is just an example of what your Firefox screen should look like.)

Thank you for your help!

More information and further troubleshooting steps can be found in the Troubleshoot Firefox crashes (closing or quitting unexpectedly) article.