I agree. Luckily for me I don't have too many tags that have slashes in them, but I can imagine if almost all your tags include slashes it's very annoying.
Currently the Firefox and Safari web clippers are both at version 6.13.2, which is from October 2017 (while the Chrome version was updated just a few days ago). It seems to me that the new version (7.x) is not compatible with Firefox or Safari, and because the Chrome version has almost 25 times the amount of users compared to the Firefox version (5,187,092 vs 221,140) Evernote won't be spending too much time making it compatible. Our only hope is that when they make version 8 of the clipper that they make it compatible with other browsers.