It's not FUD but there's usually more to it than just "Firefox". Usually has something to do with security plugins. There are sites that do not work properly with Ublock or Noscript installed, even when you turn them off for the site. I've experienced it many, many times. It happens to me most often ordering food, because a lot of local restaurants sites are janky as fuck, but I've also had issues with more well known sites. Southwest airlines has been problematic for a couple years now. My credit union also had issues with parts of their online banking app, but that thankfully got fixed after a year or two.

TL;DR - it's a real thing.

Costco Travel login page never loads for me in Firefox. Specific sites my kids use for school don't work either. I wouldn't say it happens regularly, but often enough to be annoying.

Walmart.com didn't work for me on FF for about a week, and it did work on edge and chrome (still broken on FF when I disabled all my add ons). However, they fixed it and it works now. I think it was just a problem with the build of the website, and wasn't intentional because it definitely works now.

I think that's what's more likely - temp problems that could affect any browser until their web dev fixes it. Not anything malicious like intentionally blocking a browser.

And then, it's just Walmart. It's nothing that really mattered.

I was worried about this when I originally switched from Chrome to Firefox earlier this year but I can honestly say I haven’t found a single site that I personally use that I had to go back to Chrome for. Any issues I had with any site were related to ad blocking using uBlock or DNS based blocking I also do.

The payment provider my local council uses doesn't work on Firefox, or Safari. I have to use shitty chrome on my phone. I refuse to install it on my computer.

I have issues with twitch. Given I only watch every 3 months for the POE announcement live stream, I just open brave for that one site. I have not tried to figure out if it's my setup or not

It happens to me with some payments stores. Always need to go back to chromium based pos browser

Microsoft teams

Pizza hut

Most of my utilities online sites

dialog boxes will just fuck off. I've never gotten webRTC to work properly, though that might be configuration skill issues, and or webRTC implementation skill issues, since it seems to only work on browser, not across two different ones.

I've seen sites just load asinine layouts, borked kerning, completely fucked text handling. Just goofy shit.

In some cases i've seen sites have no download buttons on firefox. I don't know why, it's confused me a few times though.

Bambulab store

Duolingo

T-mobile would be the last specific one. I couldn't navigate to certain pages within to make plan adjustments.

The local Uber eats clone here has the submit order button off screen. Reuters on Android sometimes has the top bar of the webpage shift down over the content. A video conferencing site used by my medical provider won't connect the video. The 3rd party comment section on our local news site sometimes lays out the controls off screen. The Lemmy PWA on Android used to crash on startup (recently fixed yay!!)

FF is my daily driver and 99% of things work fine, but I've definitely found a few sites where they clearly didn't test it. I still have Chrome installed for those rare occasions I need it.

And I don't even necessarily blame Firefox for this. I used to do web dev back in the day and I remember making my shit work across multiple browsers. Maybe Firefox is doing it right and Chrome is doing it wrong, but everybody targeted Chrome because it has a zillion percent of the market.

I use firefox and keep Chrome on my PC for this reason. Off the top of my head:

I can't use Siyuan correctly, my main editor, in Firefox. It only registers the initial backspace key press.

I do telehealth, and the voice/video will not work in firefox no matter what I try.

Live-reloading for Ruby on Rails projects doesn't seem to work on firefox.

Apple Podcasts for me

TradingView

Something I've been on recently. Microsoft Teams maybe?

Firefox has been, and still is, my primary browser since before Chrome even existed so, definitely not FUD. Also, it's generally not Firefox's fault either, but instead the developers of websites that don't work in Firefox are usually doing something that isn't standards compliant.

First to come to mind is that I can't log into the account management part of the pet boarding company I use when in Firefox. Another scenario is that a lot of movie streaming sites won't give Firefox video higher than 720p so in that case, Edge is often the only browser that can receive 1080p video. From my understanding the movie studios are the ones to blame for this.

Start page

Dev tools were borked on FF for me. Entire tab was blank

That's what I do and I haven't had a problem since.

This breaks any site that uses CloudFlare's Turnstile for me. It will loop forever and never let me through if my user agent is set to Chrome.

My insurance site (MyCigna) started working a couple months ago, but for years it failed to log in. It's those types of contracted apps that seem to fail the most for me, like apps you'd see on a company intranet.

Libredirect extension will redirect to public proxitok instances so you could watch them without going to tiktoks site directly

The only problem I run into is sites that use Bluetooth or USB APIs to talk to a local device. Both Firefox and Safari don't implement them due to security concerns.

T mobiles website is the most recent I had issues with. Navigating to certain pages within t mobiles site would cause "something went wrong" or just a redirect loop.

My home system. I'm not doing any extra security on it, either.