One example that I can give is that when Firefox has been running for long time, especially in Private window, the memory usage of "main" processes will grow a lot (normal & GPU). Compacting memory via about:memory does free up a bit but Chrome in similar situation will use a lot less memory. This does slow down Firefox (especially in system where you don't necessarily have a lot of memory), restarting it will make it a lot snappier.

For example I currently have Firefox & Chrome sessions which have been open for about a month on my laptop (16GB of memory). I closed every tab and only left the "blank" page open. Firefox's process manager shows 4GB GPU usage, a bit under 1GB usage for Firefox & about 250MB for extensions. After clicking "minimize memory usage" the GPU memory dropped to 3GB and Firefox process memory usage dropped by about 50MB.

For comparison Chrome uses 400MB of GPU, about 200MB for "Browser", ~150MB for for "utility" processes and about 100MB for extensions (extension list is different so we can ignore the memory usage difference for them, listed it just for completeness sake).

Despite this I do use Firefox as my primary browser.