I don't see the issue in Firefox when I have safemode turned off.

I can reproduce with safemode on (I set some CSS on the infoboxes in console to make them float right in the absence of Common.css).

The div that actually applies the column styles seems to respect the intruding floating content.

But the ol contained inside it does not.

It seems instead to be respecting .reflist's width, which contains both .mw-references-wrap div which contains the ol........

Eyeballing the list of gadgets I have turned on doesn't explain the discrepancy, nor does what's in Common/Vector/Vector-2022.css.

Firefox's multicolumn implementation doesn't like something about the width expansion button?

I can reproduce it when logged out too.

Logged out and playing with zoom, I can reproduce the overlap at 4 columns without safemode turned on, but not 3 or 5+ (i.e. both 3 and 5 take into account expected width). The above shots are clearly with 3.

I can't replicate this in the latest Firefox. Is this still an issue? It seems most likely this was an issue with the article content.

I can.

This is just float collision. When floats 'collide' with other layout boxes, the layout algorithm looks at the dimensions of the top of the colliding boxes. The top of the reflist layout here fits nicely next to the very narrow rocket image. Then AFTER the rocket image, you have this much wider image, but because it's top is below the top of the reflist, it's 'too late' to make additional space for that box, so they overlap.

Don't put multiple float elements on a side in an order that increases in width. In articles like this with an ungodly amount of data in side boxes, it's probably better to put the images as horizontal inline galleries inside the main content.