Summary: Save webpages to your computer instead.
I have 663 bookmarks saved, and I'm still trying to clean up the mess. It used to be over 1,000.
Recently, I installed an extension to check for broken URLs, as I noticed a lot of my bookmarks (some of them go all the way back to 2008) led to broken sites, expired domains, or worse, domains that expired and redirected to a malware/scam site.
The extension found about 500 broken or redirecting URLs, and I was able to quickly clean them up, but some of them I remembered well and was saddened to see the articles gone or the sites vanished completely. I checked a few of them against Wayback Machine and unfortunately, most of them never got archived. The few that did, it was a very slow and broken experience. Wayback Machine is absolutely great and I respect the dedicated people at archive.org, however it definitely has trouble sometimes.
This got me thinking about how this problem will just keep happening - sites and pages will continue to vanish without a trace, and those pages that I bookmarked for perpetuity are constantly at risk.
So, I stopped bookmarking anything I wanted to keep for the future. I used OneNote's web clipper to save the pages straight to OneNote, and then when I switched to Safari I started using the handy Export to PDF feature under the File menu. Chrome and the new Edge based on Blink both have a way to save web archives of pages, complete with images.
In addition, the content of the PDFs are searchable on macOS through Spotlight, which is fantastic. From my initial tests, .mhtml files are not, and I'm not sure how to rectify that.
Unfortunately, I also bookmark a lot of sites that provide a service or tool, and since a lot of those are proprietary, once they go down, they're gone. There's no way to save them to your computer and retain functionality unless the repository is hosted somewhere. That's one of the biggest benefits of open source to me, the code has a greater chance of survival.