i have looked into the svg files and found it might be the transform attribute of the svg tags that causes this bug. chromium based browsers ignore it while firefox does not.

however, batch export the svg files is really time consuming, so i have written a javascript to repair the already exported files by removing 'transform' from svg tags.

// repairsvg.js
((cheerio, fs) => {
    let repair = path => fs.readFile(path, 'utf8', (err, data) => err ? console.log(err) : ($ => {
        $('svg').each((i, element) => $(element).attr('transform', null));
        fs.writeFile(path + '.repaired.svg', $.html(), 'utf8', err => err ? console.log(err) : null);
    })(cheerio.load(data, {
        xmlMode: true
    })));
    fs.readFile(process.argv[2], 'utf8', (err, data) => err ? console.log(err) : (data => 
        data.split('\0').forEach(path => repair(path))
    )(data));
})(require('cheerio'), require('fs'));

save the script above as 'repairsvg.js' and put it into the directory where you exported svg files to

% pushd /path/to/svg/files
% yarn add cheerio
% find -L -name '*svg' -print0 > ./list.txt
% node ./repairsvg.js ./list.txt

now wait for a few seconds and the svg files will be repaired (this takes much less time than exporting the svg files again)