Opera sucks because, google tries to push it out of market by making sites that doesn't work quite well with opera. For example take a look here. Try to zoom in. You will see how some roads disappear. Picasaweb in opera loads for ages.
Also sometimes waiting for download to start on SourceForge, can take ages.
Some other sites also have problems.
Opera Extensions.... it's just a joke.
On positive side, Opera have fixed X11 UI. It's better than ever.
Firefox sucks, because it doesn't have any feature you'd expect from browser by default. Many default settings suck as well.
I set these options
browser.backspace_action = 0
browser.cache.disk.capacity = 0
browser.cache.disk.enable = 0
browser.cache.offline.capacity = 0
browser.download.manager.scanWhenDone = false # this one is useless on unix, so disable it :)
browser.formfill.enable = false
browser.fullscreen.animateUp = 0
browser.fullscreen.autohide = false
browser.link.open_newwindow = 1
browser.link.open_newwindow.restriction = 0
browser.search.openintab = false
browser.sessionstore.enabled = false
browser.shell.checkDefaultBrowser = false
browser.tabs.animate = false
browser.tabs.closeButtons = 2
browser.tabs.closeWindowWithLastTab = false
browser.tabs.tabMinWidth = 50
layout.spellcheckDefault = 2
network.cookie.cookieBehavior = 2
network.cookie.lifetime.days = 7
network.http.max-connections = 96
network.http.max-connections-per-server = 32
network.http.pipelining = true
network.http.pipelining.maxrequests = 8
network.http.pipelining.ssl = true
network.http.proxy.pipelining = true
zoom.maxPercent = 800
zoom.minPercent = 5
browser.tabs.insertRelatedAfterCurren = false
dom.ipc.plugins.enabled = false
If you need anything non-default, you need to install add-ons.
Why did you remove RSS icon from address bar? (Yes you can add RSS button, I know. It was simply stupid decision)
OpenSearch is probably the best idiotic idea... All alone it would be fine, if user could simple add new searches. But no, in firefox, you need to either find and install some addon (don't know any), or find site that will generate dam xml opensearch plugin. Or simply write your own xml file, then write some small html, that includes your xml, so you can import this search in firefox. Isn't that just stupid? Firefox developers, take a break and look how nicely Opera and Chrome handles this. You simply add new text string with %s in it, and all the magic works(tm).
Writing extensions for firefox seams harder, than writing extensions for chrome. I say this, because I wrote 1 extension (same functionality) for both Firefox and Chrome.
firefox 7, is out. Great.... Now I can't stop it from telling me that I don't have flash.... wtf. I don't use it, don't want it, don't need it.
Chrome sucks because it is very annoying. All dam popups are opened in new window (who on earth thought it's a good idea?). When you close last tab, chrome will terminate...
Chrome, doesn't support RSS at all (unless you install addon, extension or whatever you call it. All the same).
Sometimes when you load many pages, Chrome can lag. I even had Chrome crash because it ate all the RAM I had on my laptop (with 2GB ram)
And what about this Native Client stuff. Do we really need this?
On the bright side, Google does pay cash for finding and fixing bugs. That is very positive.
Also some sites load for ages, just because some dam web advertisement host that site use lags or doesn't respond. That's insane
IE is good browser to find better browser and download it. Yes I'm joking. I only use IE to download Opera and/or Firefox before I install them.
I don't use Safari, it works on Mac and Windows. I don't have Mac (I think it's overpriced) and I don't use Windows (unless it's in VirtualBox).
In the end
There are many, many other personal reasons, why each and every browser suck. I mentioned some of mine, which annoy me most. Perhaps you could/should share yours.
In the end I use Opera most of the time, rarely FireFox, sometimes Chrome. I hope one day we will have decent browser.