I run 2 machines 1 Linux Ubuntu 17.04, one 16.04.
The 17.04 ran well, however, it keeps spitting out links as redirects even though they are the same exact address. That's not a big deal, but I had to run it several times to get broken links completely. As for slow internet being a problem...thats not exactly right. I ran the 17.04 machine that had 1400+ bookmarks and it ran pretty quickly (did seem to hang on the last 20 though). When that machine was done I went to the other machine which has same internet connection and 1843 bookmarks and after 15mins it has scanned 15, so its not internet (I verified all was ok with my connection which is very fast). The only difference is that the machine that went fast is fairly new with 16 gigs of memory while the one that doesnt seem to want to get past 15 has only 4 and a slower processor. This tells me there may be a problem hogging memory. I hope this helps the author of this add on since I have been searching for something just like this for a long time. Thank you for your work so far!

Edit: I created a new clean profile with this add on as the only add on with the slow machine and imported my bookmarks and its working, so there must be a compatibility issue with other add ons