Take a look at Github's redesign in Firefox. Button and icon alignment are generally off by 1-2px everywhere because of it. Guessing they're just living with it because Firefox is down in the single-digit percentages of browsershare these days.
It's impossible to vertically align Helvetica consistently in Firefox and Chrome without some browser-specific adjustments, but Arial works fine.
Say I render a font with no anti-aliasing on an embedded device, because it's marginally more expensive to do so. If I did anti-alias it, you have to account for possibly growing the bitmap size to do so. If I did, am I no longer compliant with web standards? No, because the web standards don't specify dimension requirements for text nodes from source fonts.
Further, there are multiple different types of ways to anti-alias. Should the web standards dictate how?
The annoying aspect to me isn't the change in dimensions, but the inaccurate baselines. If we could reliably align text based on its baseline it wouldn't be an issue. "align-items: baseline" would be brilliant if it actually worked cross-browser.
It's pretty telling that Github doesn't even bother to solve the issue in their redesign, they've seemed to write off Firefox text alignment idiosyncrasies.
In truth, that type of work would require you to know the output sizes across every supported browser.