When I am on a SE site on the stackexchange.com domain, and go to a site with its own domain such as MathOverflow, Ask Ubuntu, or Server Fault using the links in “Your Communities” or “More Stack Exchange Communities” under the right-most menu on the top-bar,

I do not end up with the usual https://mathoverflow.net URL, but with a strange URL such as

https://mathoverflow.net/?_gl=1*i2ckzl*_ga*MTc4NjgzMTAxMS4xNTQ3NjY2ODIx*_ga_S812YQPLT2*MTY2MzkzNzc4My41MC4xLjE2NjM5Mzk0MDAuMC4wLjA.

The string is different each time. The same happens when I go from MathOverflow to MathOverflow Meta or vice versa, but not when I go to sites on the stackexchange.com domain.

I’m using Firefox 105 on Linux; I checked it also happens in Chromium. Another user reported he could not reproduce it, so it may depend on some settings.

What is the meaning of this? Is it a bug?

Originally reported on MO meta, but I’m reposting it here after realizing it does not affect only MathOverflow.