For the page loading issues, the next time it occurs press Ctrl+Shift+E to open up the DevTools' Network tab, click on the cog and enable "Persist logs" and then refresh the page and see what happens. You should be able to see why it's not loading there, for example if it's uBlock Origin blocking something from loading it will say that in the "Transferred" column (and any other network error too). You can also try refreshing with the "Disable cache" option enabled, maybe it's a caching problem, though be sure to turn that off again when you're done (I think it persists).

As for the captcha thing, if you have some of the more stringent tracking protection settings enabled it's likely you'll see more captchas simply because it relies on tracking to do its job. I had a website the other day captcha me about 5 times in a row before it let me through. The internet is just broken in this way, it's not really Firefox's fault.

If you're having other problems I may also suggest opening the browser's console with Ctrl+Shift+J, though it is very noisy and can be difficult to distinguish what's actually a problem and what isn't, sometimes it can be useful.

I believe via about:troubleshooting you can restart the browser in safe mode which temporarily launches it without any extensions. Almost every issue I have had with Firefox came down to a poorly-behaving extension (or a site that does not work well with a particular one). I've also had some Linux specific issues, but in general I don't have any of the symptoms you've seen at all.

DarkReader broke a number of sites for me (even when supposedly "off" for said sites)

uBlock Origin has broken stuff before but usually because of a non-default setting or too many enabled blocklists.

Firefox does have its own blocking / tracking protection that can break sites and that happens to me periodically. I would check that too.

User Agent Switch to Chrome.

I've had to do this with increasing regularity to fix stuff. The IE6 2.0 era is upon us.

Clearly some people haven't read the OP.

I've tried disabling all the plugins, but it still won't work.

There are too many variables here, the best troubleshooting method would be to nuke it.

This is what I would do:

1. Take a note of 2/3 sites that reliably cause problems
2. Reinstall a clean copy of Firefox, don't sign in and don't install any extensions.
3. Test those sites. If it still fails, consider filing a bug with Mozilla.
4. Install the extensions one at a time, testing those sites before adding the next one. When you find the one that breaks it, remove it (not disable) and retest. Then continue with the rest. This will tell you which extensions (if any) are responsible.
5. Sign in to your Firefox and retest. This will tell you if your settings are to blame.

Step 4 isn't perfect as the extensions might conflict in weird ways, e.g. Privacy badger and sponsorblock work individually but conflict when installed together.

Best of luck!

I definitely think there's definitely issue with your extensions at play -- while my firefox experience isn't perfect, I don't have the latter two issues you describe at all. I use both SponsorBlock and uBlockOrigin, so I would look into the other extensions (or some other privacy settings) to see if they're interfering with certain sites. Especially the captcha/login issues I can see being caused by this.

Login issues: Certain websites simply won't log me in. They'll just return an error message such as "A technical error occurred. Try again later." On other browsers, it'll log me in fine.

Does it persist after trying to login again in Firefox?
I have the problem logging into GitHub and one other website that it says error logging in but after just reloading the page I'm logged in anyways. I suspect it's an extension or an internal setting that I changed. But I haven't tried to find the cause by using a new profile or selectively disabling extensions.

Lately I noticed that Youtube sometimes is unreliable on Firefox, I think it’s just Google trying to force you to use Chrome. Until maybe a year ago I thought website compatibility w/ Firefox was generally excellent, I do think many of them aren’t testing on it now.

I'm interested to see what other people have to say about this, I've also experienced pages not loading on a variety of devices running Firefox, for years. I've tried a bunch of things but rebooting the device is the only thing that seems to consistently fix the issue.

Hi! I run Firefox on Mac and Android along with Mozilla VPN. I haven't really seen what you're describing but most often the things that interfere with my browsing are the VPN and Privacy Badger (which is much more aggressive than uBlock). Other than other recommendations, have you tried incognito windows without any addons to see if that solves the issue?

Have you tried creating a fresh firefox profile? The oddest issues I have seen with firefox users over the years are those who have carried over the same profile for a while.

Try it with a different OS-level user, who would have a totally vanilla config of Firefox with no extensions. If you still get those problems, consider that something might be tampering with your network traffic, like firewall software, or router middleware.

I don’t really have any issues like you described using Firefox on Mac. The only add on i have installed is ublock origin with default lists.

I think before trying anything else, you should disable all of your addons and try to see if you still experience the same issues and if not, start enabling your addons one at a time and retest until you find which addon could be the culprit.

I don't necessarily have the whole page not loading, but after recently switching to firefox, I'm still tuning my plugin exclusions for sites that don't work with some of the blocking in place. In addition to whatever plugins you have, there is also tracking protection built in to Firefox that I have to sometimes turn off, but it's in a different place than the extensions: the shield to the left of the URL.

Based on my experiencing with scraping websites this is almost definitely due to your ad blocking and privacy extensions, and the interesting thing is how your remote profile is built based on your IP and other fingerprints. If you were to disable all your plugins for a while (a few hours probably) most of these issues would go away. Odds are good that you can test this by enabling a VPN as well briefly. If that works, all I can suggest if you want to keep all the extensions is whitelisting sites where you have problems, especially with privacy badger which is the most problematic of them.

Sometimes the green captcha checkmark will appear after doing the "are you a human" thing, then it will just try to re-captcha me endlessly

This happened to me recently and it went away after I disabled ublock origin temporarily for a cloudflare page.

I hit something similar to the first issue. It was caused because some version of firefox had a corruption issue around localstorage/cache. The bug was fixed long ago but they didn't do anything for recovering already corrupted data. In cases where the data corruption occurred firefox would fail to load local storage data and just stay on a blank page like you described. In that case a vague error message would pop up in dev tools and the only way to fix it was to clear site data (Click lock icon on URL bar and select "Clear cookies and site data") or clear everything/make a new profile. If it was a website you visited years ago but hadn't visited since it's possibly the same issue.