Do you optimise for Firefox or just focus on Chrome / Safari?

I’m curious how often devs here ever encounter browser-specific issues and at which point you decide to just ‘leave things’ if the issue is on a relatively unused browser.

For example - About 3/4 of the way through my current site build (the 9th ‘section’) after the Course Curriculum header, I have 2 cards I built, which should flip when you click on the plus sign, and flip back when you click on the minus sign. These interactions seem to work fine in Chrome and Safari, but in firefox the glitch (pictured below) occurs. As you can see, the front of the card is present on the back, including the minus sign, and both buttons then cannot be clicked or interacted with.

With glitches and bugs which affect the site in all browsers, it’s a bit easier to commit to changing and editing things to try and solve it - but in this case I’m more hesitant, as I don’t want to mess up how it looks currently on chrome / safari. Does anyone have advice, for either my specific issue or solving-for-browser more generally?

My read-only is:

The glitch is pictured below: